BIOLOGY 
LIBRARY 


A    COLLEGE    TEXT-BOOK 


OF 


.  BOTANY 


BEING  AN  ENLARGEMENT  OF  THE  AUTHOR'S 
"ELEMENTARY  BOTANY" 


BY 

GEORGE    FRANCIS    ATKINSON,     Pn.B, 

Professor  of  Botanv  in  Cornell  University 


SECOND    EDITION,    REVISED 


NEW  YORK 
HENRY    HOLT    AND    COMPANY 


BIOLOGY 

LIBRARY 

G 


Copyright,  1905, 

BY 

HENRY  HOLT  AND  COMPANY 


PREFACE. 

THE  present  book  is  the  result  of  a  revision  and  elaboration 
of  the  author's  "  Elementary  Botany,"  New  York,  1898.  The 
general  plan  of  the  parts  on  physiology  and  general  morphology 
remains  unchanged.  A  number  of  the  chapters  in  the  physio- 
logical part  are  practically  untouched,  while  others  are  thoroughly 
revised  and  considerable  new  matter  is  added,  especially  on  the 
subjects  of  nutrition  and  digestion.  The  principal  chapters 
on  general  morphology  are  unchanged  or  only  slightly  modified, 
the  greatest  change  being  in  a  revision  of  the  subject  of  the 
morphology  of  fertilization  in  the  gymnosperms  and  angiosperms 
in  order  to  bring  this  subject  abreast  of  the  discoveries  of  the 
past  few  years.  One  of  the  greatest  modifications  has  been  in 
the  addition  of  chapters  on  the  classification  of  the  algae  and 
fungi  with  studies  of  additional  examples  for  the  benefit  of  those 
schools  where  the  time  allowed  for  the  first  year's  course  makes 
desirable  the  examination  of  a  broader  range  of  representative 
plants.  The  classification  is  also  carried  out  with  greater  definite- 
ness,  so  that  the  regular  sequence  of  classes,  orders,  and  families 
is  given  at  the  close  of  each  of  the  subkingdoms.  Thus  all  the 
classes,  all  the  orders  (except  a  few  in  the  algae),  and  many  of 
the  families,  are  given  for  the  algae,  fungi,  mosses,  liverworts, 
pteridophytes,  gymnosperms,  and  angiosperms. 

But  by  far  the  greatest  improvement  has  been  in  the  complete 
reorganization,  rewriting,  and  elaboration  of  the  part  dealing 
with  ecology,  which  has  been  made  possible  by  studies  of  the 
past  few  years,  so  that  the  subject  can  be  presented  in  a  more 
logical  and  coherent  form.  As  a  result  the  subject-matter  of 

iii 


IV  PREFA  CE. 

the  book  falls  naturally  into  five  parts,  which  may  be  passed 
in  review  as  follows: 

Part  I.  Physiology.  This  deals  with  the  life  processes  of  plants, 
as  absorption,  transpiration,  conduction,  photosynthesis, .nutrition, 
assimilation,  digestion,  respiration,  growth,  and  irritability. 
Since  protoplasm  is  fundamental  to  all  the  life  work  of  the 
plant,  this  subject  is  dealt  with  first,  and  the  student  is  led 
through  the  study  of,  and  experimentation  with,  the  simpler  as 
well  as  some  of  the  higher  plants,  to  a  general  understanding 
of  protoplasm  and  the  special  way  in  which  it  enables  the  plant 
to  carry  on  its  work  and  to  adjust  itself  to  the  conditions  of  its 
existence.  This  study  also  serves  the  purpose  of  familiarizing 
the  pupil  with  some  of  the  lower  and  unfamiliar  plants. 

Some  teachers  will  prefer  to  begin  the  study  with  general 
morphology  and  classification,  thus  studying  first  the  represen- 
tatives of  the  great  groups  of  plants,  and  others  will  prefer  to 
dwell  first  on  the  ecological  aspects  of  vegetation.  This  can 
be  done  in  the  use  of  this  book  by  beginning  with  Part  II  or 
with  Part  III. 

But  the  author  believes  that  morphology  can  best  be  com- 
prehended after  a  general  study  of  life  processes  and  functions 
of  the  different  parts  of  plants,  including  in  this  study  some  of 
the  lower  forms  of  plant  life  where  some  of  these  processes  can 
more  readily  be  observed.  The  pupil  is  then  prepared  for  a 
more  intelligent  consideration  of  general  and  comparative 
morphology  and  relationships.  Even  more  important  is  a  first 
study  of  physiology  before  taking  up  the  subject  of  ecology. 
The  great  value  to  be  derived  from  a  study  of  plants  in  their 
relation  to  environment  lies  in  the  ability  to  interpret  the  dif- 
ferent states,  conditions,  behavior,  and  associations  of  the  plant, 
and  for  this  physiology  is  indispensable.  It  is  true  that  a  con- 
siderable measure  of  success  can  be  obtained  by  a  good  teacher 
in  beginning  with  either  subject,  but  the  writer  believes  that 
measure  of  success  would  be  greater  if  the  subjects  were  taken 
up  in  the  order  presented  here. 

Part  II.  Morphology  and  lije  history  of  representative  plants. 


PREFA  CE.  V 

This  includes  a  rather  careful  study  of  representative  examples 
among  the  algae,  fungi,  liverworts,  mosses,  ferns  and  their 
allies,  gymnosperms  and  angiosperms,  with  especial  emphasis 
on  the  form  of  plant  parts,  and  a  comparison  of  them  in  the 
different  groups,  with  a  comparative  study  of  development, 
reproduction,  and  fertilization,  rounding  out  the  work  with  a 
study  of  life  histories  and  noting  progression  and  retrogression 
of  certain  organs  and  phases  in  proceeding  from  the  lower  to  the 
higher  plants.  Thus,  in  the  algae  a  first  critical  study  is  made 
of  four  examples  which  illustrate  in  a  marked  way  progressive 
stages  of  the  plant  body,  sexual  organs,  and  reproduction.  Addi- 
tional examples  are  then  studied  for  the  purpose  of  acquiring  a 
knowledge  of  variations  from  these  types  and  to  give  a  broader 
basis  for  the  brief  consideration  of  general  relationships  and 
classification. 

A  similar  plan  is  followed  in  the  other  great  groups.  The 
processes  of  fertilization  and  reproduction  can  be  most  easily 
observed  in  the  lower  plants  like  the  algae  and  fungi,  and  this 
is  an  additional  argument  in  favor  of  giving  emphasis  to  these 
forms  of  plant  life  as  well  as  the  advantage  of  proceeding  logic- 
ally from  simpler  to  more  complex  forms.  Having  also  learned 
some  of  these  plants  in  our  study  of  physiology,  we  are  following 
another  recognized  rule  of  pedagogy,  i.e.,  proceeding  from 
known  objects  to  unknown  structures  and  processes.  Through 
the  study  of  the  organs  of  reproduction  of  the  lower  plants  and 
by  general  comparative  morphology  we  have  come  to  an  under- 
standing of  tb.3  morphology  of  the  parts  of  the  flower,  and  of 
the  true  sexual  organs  of  the  seed  plants,  and  no  student  can 
hope  to  properly  interpret  the  significance  of  the  flower,  or  the 
sexual  organs  of  the  seed  plants  who  neglects  a  careful  study 
of  the  general  morphology  of  the  lower  plants. 

Part  III.  Plant  members  in  relation  to  environment.  This  part 
deals  with  the  organization  of  the  plant  body  as  a  whole  in  its 
relation  to  environment,  the  organization  of  plant  tissues  with 
a  discussion  of  the  principal  tissues  and  a  descriptive  synopsis  of 
the  same.  This  is  followed  by  a  complete  study  from  a  biological 


VI  PREFACE. 

standpoint  of  the  different  members  of  the  plant,  their  special 
function  and  their  special  relations  to  environment.  The  stem, 
root,  leaf,  flower,  etc.,  are  carefully  examined  and  their  ecological 
relations  pointed  out.  This  together  with  the  study  of  physiology 
and  representatives  in  the  groups  of  plants  forms  a  thorough 
basis  for  pure  plant  ecology,  or  the  special  study  of  vegetation 
in  its  relation  to  environment. 

Part  IV.  Vegetation  in  relation  to  environment.  This  part 
deals  with  pure  plant  ecology  in  its  general  aspects,  or  vegetation 
forms  in  relation  to  environment.  First  there  is  a  study  of  the 
factors  of  environment  or  ecological  factors,  which  in  general 
are  grouped  under  the  physical,  climatic,  and  biotic  factors. 
This  is  followed  by  the  laws  of  migration,  the  analysis  of  vegeta- 
tion forms  and  structures,  plant  formations  and  societies.  Then 
in  order  are  treated  forest  societies,  prairie  societies,  desert 
societies,  arctic  and  alpine  societies,  aquatic  societies,  and  the 
special  societies  of  sandy,  rocky,  and  marshy  places.  This 
part  closes  with  some  practical  suggestions  for  the  study  of  plant 
formations,  and  a  description  of  the  principal  vegetation  regions 
of  the  earth. 

Part  V.  Representative  families  oj  angiosperms.  Topics  for 
study  of  additional  examples  of  angiosperms  are  outlined  here. 
It  is  not  intended  that  this  shall  follow  Part  IV  in  the  course, 
but  where  the  teacher  desires  to  study  more  examples  than  are 
given  in  Part  II  these  topics  or  chosen  ones  can  be  studied  along 
with  or  following  Part  III.  The  work  of  Part  IV  can  usually 
be  well  undertaken  by  field  excursions  in  conjunction  with  the 
work  of  Part  III,  and  this  would  naturally  be  handled  in  the 
spring,  with  Part  I  in  the  autumn  and  Part  II  in  the  winter. 

Acknowledgments.  The  author  wishes  to  express  his  grate- 
fulness to  all  those  who  have  given  aid  in  the  preparation  of  this 
work,  or  of  the  earlier  editions  of  Elementary  Botany;  to  his 
associates,  Dr.  E.  J.  Durand,  Dr.  K.  M.  Wiegand,  and  Professor 
W.  W.  Rowlee,  of  the  botanical  department,  and  to  Professor 
B.  M.  Duggar  of  the  University  of  Missouri,  Professor  J.  C. 
Arthur  of  Purdue  University,  and  Professor  W.  F.  Ganong  of 


PREFACE.  Vll 

Smith  College,  for  reading  one  or  more  portions  of  the  text; 
as  well  as  to  all  those  who  have  contributed  illustrations. 

Illustrations.  The  large  majority  of  the  illustrations  are  new 
(or  are  the  same  as  those  used  in  earlier  editions  of  the  author's 
Elementary  Botany)  and  were  made  with  special  reference  to 
the  method  of  treatment  followed  in  the  text.  Many  of  the 
photographs  were  made  by  the  author.  Others  were  contributed 
by  President  P.  H.  Mell  of  the  Clemson  Agricultural  College; 
Professor  Rowlee  of  Cornell  University;  Mr.  H.  J.  Webber, 
Washington,  D.  C.;  Mr.  John  Gifford  of  New  Jersey;  Professor 
B.  M.  Duggar,  University  of  Missouri;  Mr.  Herman  von  Schrenk, 
Missouri  Botanical  Garden;  Professor  H.  C.  Cowles  of  the 
University  of  Chicago;  Professor  C.  E.  Bessey,  University  of 
Nebraska;  Dr.  M.  B.  Howe,  New  York  Botanical  Garden; 
Mr.  Gifford  Pinchot,  Chief  of  the  Bureau  of  Forestry;  Mr.  B.  T. 
Galloway,  Chief  of  the  Bureau  of  Plant  Industry;  Professor  Tre- 
lease,  Missouri  Botanical  Garden;  Professor  Tuomey  of  Yale 
University;  and  Mr.  E.  H.  Harriman,  who  through  Dr.  C.  H. 
Merriam  of  the  National  Museum  allowed  the  use  of  several 
of  his  copyrighted  photographs  from  Alaska.  To  those  who 
have  contributed  drawings  the  author  is  indebted  as  follows:  to 
Professor  Margaret  C.  Ferguson,  Wellesley  College;  Professor 
Bertha  Stoneman  of  Huguenot  College,  South  Africa;  Mr.  H. 
Hasselbring  of  Chicago;  Dr.  K.  Miyake,  formerly  of  Cornell 
University  and  now  of  Doshisha  College,  Japan;  and  Pro- 
fessors Ikeno  and  Hirase  of  the  Tokio  Imperial  University. 
The  author  is  also  indebted  to  Ginn  &  Co.,  Boston,  for  the 
privilege  to  use  from  his  "  First  Studies  of  Plant  Life  "  the  fol- 
lowing figures:  28,  29,  46,  48,  49,  56,  62,  66,  67,  87,  102,  103, 
422-426,  429,  430,  438-440,  443,  444,  448,  449,  452>  472~475>  4^6, 
4966,  5140,  5146.  A  few  others  are  acknowledged  in  the  text. 

CORNELL  UNIVERSITY,  January,  1905. 


TABLE  OF  CONTENTS. 

PART  I.    PHYSIOLOGY. 
CHAPTER  I. 

PAGB 

PROTOPLASM .1 i 

CHAPTER  II. 
ABSORPTION,  DIFFUSION,  OSMOSE 13 

CHAPTER  III. 
How  PLANTS  OBTAIN  WATER 22 

CHAPTER  IV. 
TRANSPIRATION,  OR  THE  Loss  OF  WATER  BY  PLANTS 35 

CHAPTER  V. 
PATH  OF  MOVEMENT  OF  WATER  IN  PLANTS 48 

CHAPTER  VI. 
MECHANICAL  USES  OF  WATER 56 

CHAPTER  VII. 

STARCH  AND  SUGAR  FORMATION 60 

1.  The  Gases  Concerned 60 

2.  Where  Starch  is  Formed 64 

3.  Chlorophyll  and  the  Formation  of  Starch 67 

CHAPTER  VIII. 

STARCH  AND  SUGAR  CONCLUDED;  ANALYSIS  OF  PLANT  SUBSTANCE..  . .  73 

1.  Translocation  of  Starch 73 

2.  Sugar,  and  Digestion  of  Starch 75 

3.  Rougk  Analysis  of  Plant  Substance 79 

ix 


X  TABLE   OF  CONTENTS. 

CHAPTER  IX. 

PAGE 

How  PLANTS  OBTAIN  THEIR  FOOD,  1 81 

1.  Sources  of  Plant  Food 81 

2.  Parasites  and  Saprophytes 83 

3.  How  Fungi  Obtain  their  Food 86 

4.  Mycorhiza 91 

5.  Nitrogen-gatherers 92 

6.  Lichens 93 

CHAPTER  X. 

How  PLANTS  OBTAIN  THEIR  FOOD,  II 97 

Seedlings,  97.     Digestion,  107.     Assimilation 109 

CHAPTER  XI. 
RESPIRATION no 

CHAPTER  XII. 
GROWTH 118 

CHAPTER  XIII. 
IRRITABILITY 125 

PART   II.     MORPHOLOGY   AND   LIFE   HISTORY 
OF  REPRESENTATIVE  PLANTS. 

CHAPTER  XIV. 
SPIROGYRA. 136 

CHAPTER  XV. 
VAUCHERIA. 142 

CHAPTER  XVI. 
(EDOGONIUM 147 

CHAPTER  XVII. 

COLEOCaffiTE. 153 

CHAPTER  XVIII. 
CLASSIFICATION  AND  ADDITIONAL  STUDIES  OF  THE  ALG.E. 158 

CHAPTER  XIX. 
FUNGI  :   MUOOR  \NT>  SAPROLEGNIA 177 


TABLE  OF  CONTENTS.  xl 

CHAPTER  XX. 

PAGE 

FUNGI  CONTINUED  ("  Rusts  "  Uredineae) 187 

CHAPTER  XXI. 
THE  HIGHER  FUNGI 195 

CHAPTER  XXII. 
CLASSIFICATION  OF  THE  FUNGI 213 

CHAPTER  XXIII. 

LIVERWORTS  (Hepaticae) 222 

Riccia,  222.     Marchantia 226 

CHAPTER  XXIV. 

LIVERWORTS  CONTINUED — 231 

Sporogonium  of  Marchantia 231 

Leafy -stemmed  Liverworts 236 

The  Horned  Liverworts 240 

Classification  of  the  Liverworts 247 

CHAPTER  XXV. 

MOSSES  (Musci) 243 

Classification  of  Mosses 248 

CHAPTER  XXVI. 
FERNS 251 

CHAPTER  XXVII. 

FERNS  CONTINUED 262 

Gametophyte  of  Ferns 262 

Sporophyte 268 

CHAPTER  XXVIII. 
DIMORPHISM  OF  FERNS 273 

CHAPTER  XXIX. 
HORSETAILS 280 

CHAPTER  XXX. 
CLUB-MOSSES. 284 

CHAPTER  XXXI. 
QUILL  WORTS  (Isoetes) 289 


TABLE   OF  CONTENTS. 
CHAPTER  XXXII. 

PAGB 

FERNS  AND  THEIR  RELATIVES 292 

of  the  Pteridophytes 295 

CHAPTER  XXXIII. 
GYNMOSPERMS 297 

CHAPTER  XXXIV. 
FURTHER  STUD       ON  GYMNOSPERMS 311 

CHAPTER  XXXV. 
MORPHOLOGY  OF  THE  ANGIOSPERMS:   TRILLIUM;   DENTARIA 318 

CHAPTER  XXXVI. 
GAMETOPHYTE  AND  SPOROPHYTE  OF  ANGIOSPERMS 325 

CHAPTER  XXXVII. 

MORPHOLOGY  OF  THE  NUCLEUS  AND  SIGNIFICANCE  OF  GAMETOPHYTE 
AND  SPOROPHYTE 340 

PART  III.    PLANT  MEMBERS  IN  RELATION 
TO  ENVIRONMENT. 

CHAPTER  XXXVIII. 

THE  ORGANIZATION  OF  THE  PLANT 349 

I.  Organization  of  Plant  Members 349 

II.  Organization  of  Plant  Tissues 356 

CHAPTER  XXXIX. 

THE  DIFFERENT  TYPES  OF  STEMS 365 

I.  Erect  Stems . 365 

II.  Creeping,  Climbing,  and  Floating  Stems 369 

III.  Specialized  Shoots  and  Shoots  for  Storage  of  Food 372 

IV.  Annual  Growth  and  Winter  Protection  of  Shoots  and  Buds. .  .  374 

CHAPTER  XL. 

FOLIAGE  LEAVES 383 

I.  General  Form  and  Arrangement  of  Leaves 383 

II.  Protective  Modifications  of  Leaves 393 

III.  Protective  Positions 395 

IV.  Relation  of  Leaves  to  Light 397 

V.  Leaf  Patterns 404 


TABLE   OF  CONTENTS.  Xlil 

CHAPTER  XLL 

>•"  PAGE 

(  THE  ROOT Y- 410 

>  I.  Function  of  Roots [  ''t!* 410 

/  II.  Kinds  of  Roots 415 

CHAPTER  XLIL 

THE  FLORAL  SHOOT 419 

I.  The  Parts  of  the  Flower 419 

II.  Kinds  of  Flowers 421 

III.  Arrangement  of  Flowers,  or  Mode  of  Infloresa    .e 426 

CHAPTER  XLIIL 
POLLINATION 433 

CHAPTER  XLIV. 

THE  FRUIT 450 

I.  Parts  of  the  Fruit 450 

II.  Indehiscent  Fruits 451 

III.  Dehiscent  Fruits 452 

IV.  Fleshy  and  Juicy  Fruits 454 

V.  Reinforced,  or  Accessory,  Fruits 455 

VI.  Fruits  of  Gymnosperms 456 

VII.  "Fruit"  of  Ferns,  Mosses,  etc 457 

CHAPTER  XLV. 
SEED  DISPERSAL 458 


PART   IV.    VEGETATION   IN   RELATION   TO 
ENVIRONMENT. 

CHAPTER  XLVI. 

FACTORS  INFLUENCING  VEGETATION  TYPES;  OR  ECOLOGICAL  FACTORS  .  464 

I.  Physical  Factors 465 

II.  Climatic  Factors 477 

III.  Biotic  Factors 479 

CHAPTER  XLVII. 

VEGETATION  TYPES  AND  STRUCTURES 482 

I.  Warming's  Vegetation  Types 483 

II.  Schimper's  Vegetation  Types 485 

III.  Plant  Structures  adapted  to  Conditions  of  Environment 486 


XIV  TABLE    OF  CONTENTS. 

CHAPTER  XLVIII. 

PAGE 

LAWS  AND  LIMITS  OF  PLANT  MIGRATION 497 

I.  Relation  of  Plants  to  Earth's  Surface  as  a  Whole 498 

II.  Life  Regions,  Zones,  and  Areas 500 

III.  Methods  and  Causes  of  Plant  Migration 506 

CHAPTER  XLIX. 

PLANT  FORMATIONS 515 

I.  Climatic  Formations 515 

II.  Edaphic  Formations 518 

III.  Aquatic  Formations. 521 

IV.  Culture  Formations 521 

V.  Principal  and  Individual  Formations. 522 

CHAPTER  L. 

FOREST  SOCIETIES 529 

I.  General  Character  of  Forest  Societies 529 

II.  Boreal  Forests 534 

III.  Austral  Forests t. . 535 

IV.  Tropical  Forests 541 

V.  Relation  of  Forests  to  Rainfall , .  4;;  .  546 

VI.  Forest  Regeneration  and  Protection 548 

CHAPTER  LI. 

THE  PRAIRIE  AND  PLAINS  SOCIETIES 556 

I.  Grassland  Formations , 556 

II.  Prairie  Formations 557 

III.  The  Plains  Formations 559 

IV.  Edaphic  Formations  in  the  Prairie  Region 560 

CHAPTER  LII. 

DESERT  PLANT  SOCIETIES . . . 565 

I.  Characters  of  True  Desert  Plants 565 

II.  The  Sonora-Nevada  Desert 568 

III.  Other  Desert  Regions 573 

CHAPTER  LIII. 

t 

ARCTIC  AND  ALPINE  PLANT  SOCIETIES 576 

I.  Arctic  Plant  Societies 576 

II.  Alpine  Plant  Societies ...... 582 


TABLE   OF  CONTENTS.  XV 
CHAPTER  LIV 

PAGE 

THE  VEGETATION  OF  THE  STRAND 586 

I.  Types  of  Strand 586 

II.  The  Vegetation  of  the  Beach  or  Strand 588 

III.  Vegetation  of  the  Dunes 592 

CHAPTER  LV. 

PLANT  SOCIETIES  OF  ROCKY  AREAS,  MEADOWS,  AND  MARSHES 600 

I.  Vegetation  of  Rocky  Places,  and  New  Land 600 

II.  Vegetation  of  Swamps  and  Moors 606 

CHAPTER  LVI. 

AQUATIC  PLANT  SOCIETIES 620 

I.  General  Considerations 620 

II.  Fresh-water,  or  Limnetic,  Plant  Societies 624 

III.  Marine,  or  Pelagic,  Plant  Societies 627 

CHAPTER  LVII. 

PRACTICAL  STUDY  OF  PLANT  FORMATIONS 630 

I.  Suggestions  for  Practical  Study  of  Plant  Formations 630 

II.  Natural  Vegetation  Regions  of  the  Earth 638 


PART  V.    REPRESENTATIVE  FAMILIES  OF 
ANGIOSPERMS. 

CHAPTER  LVIII. 
RELATION  OF  SPECIES,  GENUS,  FAMILY,  ORDER,  ETC 648 

CHAPTER  LIX. 
MONOCOTYLEDONS 654 

CHAPTER  LX. 
MONOCOTYLEDONS  CONCLUDED 662 

CHAPTER  LXI. 
DICOTYLEDONS 667 

CHAPTER  LXII. 
DICOTYLEDONS  CONTINUED 672 


XVI  TABLE  OF  CONTENTS. 

CHAPTER  LXIII. 

PAGE 

DICOTYLEDONS  CONTINUED 678 

CHAPTER  LXIV. 
DICOTYLEDONS  CONTINUED 687 

CHAPTER  LXV. 
DICOTYLEDONS  CONCLUDED 694 

CHAPTER  LXVI. 

CLASSIFICATION  OF  THE  ANGIOSPERMS 702 

I.  Class  Monocotyledones 702 

II.  Class  Dicotyledones 704 

APPENDIX 713 

INDEX 705 


PART  I. 

PHYSIOLOGY. 

CHAPTER    I. 

PROTOPLASM.* 

1.  In  the  study  of  plant  life  and  growth,  it  will  be  found 
convenient   first    to  inquire  into  the  nature    of  the   substance 
which  we  call  the  living  material  of  plants.     For  plant  growth, 
as  well  as  some  of  the  other  processes  of  plant  life,  are  at  bottom 
dependent  on  this  living  matter.     This  living  matter  is  called  in 
general  protoplasm. 

2.  In  most   cases   protoplasm   cannot   be   seen   without   the 
help  of  a  microscope,  and  it  will  be  necessary  for  us  here  to  em- 
ploy one  if  we  wish  to  see  protoplasm,  and  to  satisfy  ourselves 
by   examination    that  the   substance  we    are    dealing   with   is 
protoplasm. 

3.  We  shall  find  it  convenient  first  to  examine  protoplasm  in 
some  of  the  simpler  plants  ;  plants  which  from  their  minute  size 
and  simple  structure  are  so  transparent  that  when  examined  with 
the  microscope  the  interior  can  be  seen. 

For  our  first  study  let  us  take  a  plant  known  as  spirogyra, 
though  there  are  a  number  of  others  which  would  serve  the  pur- 
pose quite  as  well,  and  may  quite  as  easily  be  obtained  for 
study. 

*For  apparatus,  reagents,  collection  and  preservation  of  material,  etc.,  see 
Appendix. 


PHYSIOLOGY. 


Protoplasm  in  spirogyra. 

4.  The  plant  spirogyra. — This  plant  is  found  in  the  water 
of  pools,  ditches,  ponds,  or  in  streams  of  slow-running  water. 
It  is  green  in  color,  and  occurs  in  loose  mats,  usually  floating 
near  the  surface.     The  name  "pond-scum"  is  sometimes  given 
to  this  plant,  along  with  others  which  are  more  or  less  closely 
related.      It  is  an  alga,  and  belongs  to  a  group  of  plants  known 
as  algce.     If  we  lift  a  portion  of  it  from  the  water,  we  see  that 
the  mat  is  made  up  of  a  great  tangle  of  green  silky  threads. 
Each  one  of  these  threads  is  a  plant,  so  that  the  number  con- 
tained in  one  of  these  floating  mats  is  very  great. 

Let  us  place  a  bit  of  this  thread  tangle  on  a  glass  slip,  and 
examine  with  the  microscope  and  we  will  see  certain  things  about 
the  plant  which  are  peculiar  to  it,  and  which  enable  us  to  dis- 
tinguish it  from  other  minute  green  water  plants.  We  shall 
also  wish  to  learn  what  these  peculiar  parts  of  the  plant  are,  in 
order  to  demonstrate  the  protoplasm  in  the  plant.* 

5.  Chlorophyll  bands  in  spirogyra. — We  first  observe  the 
presence  of  bands ;  green  in  color,    the  edges   of  which    are 
usually  very  irregularly  notched.     These  bands  course  along  in 
a  spiral  manner  near  the  surface  of  the  thread.     There  may  be 
one  or  several  of  these  spirals,  according  to  the  species  which 
we  happen  to  select  for  study.     This  green  coloring  matter  of 
the  band  is  chlorophyll,  and  this  substance,  which  also  occurs  in 
the  higher  green  plants,  will  be  considered  in  a  later  chapter. 
At   quite  regular  intervals  in  the  chlorophyll  band  are   small 
starch  grains,  grouped  in  a,  rounded  mass  enclosing  a  minute 
body,  the  pyrenoid,  which  is  peculiar  to  many  algae. 

6.  The  spirogyra  thread  consists  of  cylindrical  cells  end  to 
end. — Another  thing  which  attracts  our  attention,  as  we  examine 
a  thread  of  spirogyra  under  the  microscope,  is  that  the  thread  is 

*  If  spirogyra  is  forming  fruit  some  of  the  threads  will  be  lying  parallel  in 
pairs,  and  connected  with  short  tubes.  In  some  of  the  cells  there  will  be 
found  rounded  or  oval  bodies  known  as  zygospores.  These  may  be  seen  in 
fig.  86,  and  will  be  described  in  another  part  of  the  book. 


PROTOPLASM. 


made  up  of  cylindrical  segments  or  compartments  placed  end  to 
end.  We  can  see  a  distinct  separating  line  be- 
tween the  ends.  Each  one  of  these  segments  or 
compartments  of  the  thread  is  a  cell,  and  the 
boundary  wall  is  in  the  form  of  a  cylinder  with 
closed  ends. 

7.  Protoplasm.  —  Having    distinguished    these 
parts  of  the  plant  we  can  lookyfor  the  protoplasm. 
It  occurs  within   the  cells.    /It  is  colorless  (i.e., 
hyaline)  and  consequently  requires  close  observa- 
tion.     Near  the  center  of  tyie  cell  c?n  be  seen  a 
rather   dense    granular  boc^   of  an   elliptical    or 
irregular  form,  with  its  long  diameter  transverse 
to  the  axis  of  the  cell  in  some  species  ;   or  trian- 
gular, or  quadrate  in  others.      This  is  the  nucleus. 
Around  the  nucleus  is  a  granular  layer  from  whi$h 
delicate   threads  of  a   shiny    granular   substance 
radiate  in  a  starlike  manner,  and  terminate  in  the 
chlorophyll  band  at  one   of  the    pyrenoids.      A 
granular  layer    of  the  same   substance  lines   the 
inside  of  the  cell  wall,  and  can  be  seen  through 
the  microscope  if  it  is  properly  focussed.     This 
granular  substance  in  the  cell  is  protoplasm. 

8.  Cell-sap  in  spirogyra.  —  The  greater  part  of 
the  interior  space  of  the  cell,  that  between  the 
radiating  strands  of  protoplasm,  is  occupied  by 
a  watery  fluid,  the  "  cell-sap." 

9.  Reaction  of  protoplasm  to  certain  reagents. 
—We  can   employ  certain    tests  to  demonstrate 
that  this  granular  substance  which  we  have  seen 
is  protoplasm,  for  it  has  been  found,  by  repeated 
experiments  with  a  great  many  kinds  of  plants,   gyra,  showing^ong 

.1  i  .  ,    /.  .  cells,     chlorophyll 

that  protoplasm  gives  a  definite  reaction  in  re-   band,    nucleus. 

.  ,  .  .  ,     strands    of    proto- 

sponse  to  treatment  with  certain  substances  called   plasm,    and    the  . 

T  r  i  i  granular  wa»)  layer 

reagents.     Let  us  mount  a   few   threads   of  the  ot  protoplasm 
spirogyra  in  a  drop  of  a  solution  of  iodine,  and  observe  the 


PHYSIO  LOG  y. 


results  with  the  aid  of  the  microscope.  The  iodine  gives  a 
yellowish-brown  color  to  the  protoplasm,  and  it  can  be  more 
distinctly  seen.  The  nucleus  is  also  much  more  prominent 
since  it  colors  deeply,  and  we  can  perceive  within  the  nucleus 
one  small  rounded  body,  sometimes  more,  the  nucleolus.  The 
iodine  here  kills  and  stains  the  protoplasm.  The  proto- 
plasm, however,  in  a  living  condition  will  resist  for  a  time  some 

other  reagents, 
as  we  shall  see 
if  we  attempt 
to  stain  it  with 
a  one  per  cent 
aqueous  solu- 
tion of  a  dye 
known  as  eosin. 
Let  us  mount  a 
few  living 
threads  in  such 
a  solution  of 
eosin,  and  after 
Fig.  2.  Fig.  3.  a  time  wash  off 

Cell  of  spirogyra  before  treat-    Cell  of  spirogyra  after  treatment    ^^  -tain      TVip> 
ment  with  iodine.  with  alcohol  and  iodine.  stain. 

protoplasm  remains  uncolored.  Now  let  us  place  these  threads 
for  a  short  time,  two  or  three  minutes,  in  strong  alcohol,  which 
kills  the  protoplasm.  Then  mount  them  in  the  eosin  solution. 
The  protoplasm  now  takes  the  eosin  stain.  After  the  proto- 
plasm has  been  killed  we  note  that  the  nucleus  is  no  longer 
elliptical  or  angular  in  outline,  but  is  rounded.  The  strands  of 
protoplasm  are  no  longer  in  tension  as  they  were  when  alive. 

10.  Let  us  now  take  some  fresh  living  threads  and  mount 
them  in  water.  Place  a  small  drop  of  dilute  glycerine  on  the 
slip  at  one  side  of  the  cover  glass,  and  with  a  bit  of  filter  paper 
at  the  other  side  draw  out  the  water.  The  glycerine  will  flow 
under  the  cover  glass  and  come  in  contact  with  the  spirogyra 
threads.  f  Glycerine  absorbs  water  promptly.  Being  in  contact 
with  the  threads  it  draws  water  out  of  the  cell  cavity,  thus  caus- 


PROTOPLASM. 


ing  the  layer  of  protoplasm  which  lines  the  inside  of  the  cell 
wall  to  collapse,  and  separate  from  the  wall,  drawing  the 
chlorophyll  band 
inward  toward  the 
center  also.  The 
wall  layer  of  proto- 
plasm can  now  be 
more  distinctly 
seen  and  its  gran- 
ular character  ob- 
served. 

We  have  thus 
employed  three 
tests  to  demon- 
strate that  this  sub- 
stance with  which 
we  are  dealing 
shows  the  reac- 
tions which  we 
know  by  experi- 
ence to  be  given 


Cell  of  spirogyra  before 
treatment  with 


Fig.  5. 

Cells  of  spirogyra  after  treatment 
with  glycerine. 


glycerine. 

by  protoplasm.  We  therefore  conclude  that  this  colorless  and 
partly  granular,  slimy  substance  in  the  spirogyra  cell  is  proto- 
plasm, and  that  when  we  have  performed  these  experiments, 
and  noted  carefully  the  results,  we  have  seen  protoplasm. 

11.  Earlier  use  of  the  term  protoplasm. — Early  students  of  the  living 
matter  in  the  cell  considered  it  to  be  alike  in  substance,  but  differing  in 
density;  so  the  term  protoplasm  was  applied  to  all  of  this  living  matter.  The 
nucleus  was  looked  upon  as  simply  a  denser  portion  of  the  protoplasm,  and 
the  nucleolus  as  a  still  denser  portion.  Now  it  is  believed  that  the  nucleus  is 
a  distinct  substance,  and  a  permanent  organ  of  the  cell.  The  remaining  por- 
tion of  the  protoplasm  is  now  usually  spoken  of  as  the  cytoplasm. 

In  spirogyra  then  the  cytoplasm  in  each  cell  consists  of  a  layer  which  lines 
the  inside  of  the  cell  wall,  a  nuclear  layer,  which  surrounds  the  nucleus,  and 
radiating  strands  which  connect  the  nucleus  and  wall  layers,  thus  suspending 
the  nucleus  near  the  center  of  the  cell.  But  it  seems  best  in  this  elementary 
study  to  use  the  term  protoplasm  in  its  general  sense. 


6  PHYSIOLOGY. 

Protoplasm  in  mucor. 

12.  Let  us  now  examine  in  a  similar  way  another    of  the 
simple  plants  with  the  special  object  in  view  of  demonstrating 
the  protoplasm.      For  this  purpose  we  may  take  one  of  the  plants 
belonging   to  the    group   of  fungi.     These   plants    possess    no 
chlorophyll.     One    of  several   species    of  mucor,    a    common 
mould,  is  readily  obtainable,  and  very  suitable  for  this  study.* 

13.  Mycelium  of  mucor. — A  few  days  after  sowing  in  some 
gelatinous  culture  medium  we  find  slender,  hyaline  threads,  which 
are  very  much  branched,  and,  radiating  from  a  central  point,  form 
circular  colonies,  if  the  plant  has  not  been  too  thickly  sown,  as 
shown  in  fig.  6.     These   threads  of  the  fungus  form  the  myce- 
lium.    From  these  characters  of  the  plant,  which  we  can  readily 
see  without  the  aid  of  a  microscope,  we  note  how  different  it  is 
from  spirogyra. 

To  examine  for  protoplasm  let  us  lift  carefully  a  thin  block  of 
gelatine  containing  the  mucor  threads,  and  mount  it  in  water  on 
a  glass  slip.  Under  the  microscope  we  see  only  a  small  portion 
of  the  branched  threads.  In  addition  to  the  absence  of  chlo- 
rophyll, which  we  have  already  noted,  we  see  that  the  myce- 
lium is  not  divided  at  short  intervals  into  cells,  but  appears 
like  a  delicate  tube  with  branches,  which  become  successively 
smaller  toward  the  ends. 

14.  Appearance  of  the  protoplasm. — Within  the  tube-like 
thread  now  note  the  protoplasm.     It  has  the  same  general  ap- 
pearance as  that  which  we  noted  in  spirogyra.      It  is  slimy,  or 
semi-fluid,  partly  hyaline,  and  partly  granular,  the  granules  con- 
sisting of  minute  particles  (ihe-mtcrosomes).     While  in  mucor  the 
protoplasm  has  the  same  general  appearance  as  in  spirogyra,  its 
arrangement  is  very  different.      In  the   first  place  it  is  plainly 

*  The  most  suitable  preparations  of  mucor  for  study  are  made  by  growing 
the  plant  in  a  nutrient  substance  which  largely  consists  of  gelatine,  or,  better, 
agar-agar,  a  gelatinous  preparation  of  certain  seaweeds.  This,  after  the 
plant  is  sown  in  it,  should  be  poured  into  sterilized  shallow  glass  plates, 
called  Petrie  dishes. 


PROTOPLASM. 


continuous  throughout  the  tube.     We  do  not  see  the  prominent 
radiations  of  strands  around  a  large  nucleus,  but  still  the  proto- 


Fig  6. 
Colonies  of  mucor. 

plasm  does  not  fill  the  interior  of  the  threads.  Here  and  there 
are  rounded  clear  spaces  termed  vacuoles,  which  are  filled  with 
the  watery  fluid,  cell-sap.  The  nuclei  in  mucor  are  very  mi- 
nute, and  cannot  be  seen  except  after  careful  treatment  with 
special  reagents. 

15  Movement  of  the  protoplasm  in  mucor. — While  exam- 
ining the  protoplasm  in  mucor  we  are  likely  to  note  streaming 
movements.  Often  a  current  is  seen  flowing  slowly  down  one 
side  of  the  thread,  and  another  flowing  back  on  the  other  side, 
or  it  may  all  stream  along  in  the  same  direction. 

16.  Test  for  protoplasm. — Now  let  us  treat  the  threads  with 
a  solution  of  iodine.  The  yellowish-brown  color  appears  which 
is  characteristic  of  protoplasm  when  subject  to  this  reagent. 


8  PHYSIO  LOG  Y. 

If  we  attempt  to  stain  the  living  protoplasm  with  a  one  per 
cent  aqueous  solution  of  eosin  it  resists  it  for  a  time,  but  if  we 
first  kill  the  protoplasm  with  strong  alcohol,  it  reacts  quickly  to 
the  application  of  the  eosin.  If  we  treat  the  living  threads 
with  glycerine  the  protoplasm  is  contracted  away  from  the  wall, 
as  we  found  to  be  the  case  with  spirogyra.  While  the  color, 


Fig.  7- 
Thread  of  mucor,  showing  protoplasm  and  vacuoles. 

form  and  structure  of  the  plant  mucor  is  different  from  spiro- 
gyra,  and  the  arrangement  of  the  protoplasm  within  the  plant 
is  also  quite  different,  the  reactions  when  treated  by  certain  re- 
agents are  the  same.  We  are  justified  then  in  concluding  that 
the  two  plants  possess  in  common  a  substance  which  we  call 
protoplasm. 

Protoplasm  in  nitella. 

17.  One  of  the  most  interesting  plants  for  the  study  of  one  remarkable 
peculiarity  of  protoplasm  is  Nitella.     This  plant  belongs  to  a  small  group 
known  as  stoneworts.     They  possess  chlorophyll,  and,  while  they  are  still 
quite  simple  as  compared  with  the  higher  plants,  they  are  much  higher  in  the 
scale  than  spirogyra  or  mucor. 

18.  Form  of  nitella — A  common  species  of  nitella  is  Nitella  flexilis. 
It  grows  in  quiet  pools  of  water.     The  plant  consists  of  a  main  axis,  in  the 
form  of  a  cylinder.     At  quite  regular  intervals  are  whorls  of  several  smaller 
thread-like  outgrowths,  which,  because  of  their  position,  are  termed  "  leaves," 
though  they  are  not  true  leaves.     These  are  branched  in  a  characteristic  fash- 
ion at  the  tip.     The  main  axis  also  branches,  these  branches  arising  in  the  axil 
of  a  whorl,  usually  singly.     The  portions  of  the  axis  where  the  whorls  arise 
are  the  nodes.     Each  node  is  made  up  of  a  number  of  small  cells  definitely 
arranged.     The  portion  of  the  axis  between  two  adjacent  whorls  is  an  inter- 


PROTOPLASM.  9 

node.  These  internodes  are  peculiar.  They  consist  of  but  a  single  "  cell," 
and  are  cylindrical,  with  closed  ends.  They  are  sometimes  5-10  cm.  long. 

19.  Internode  of  nitella. — For   the   study   of  an   internode  of  nitella,  a 
small  one,  near  the  end,  or  the  ends  of  one  of  the  "  leaves"  is  best  suited, 
since  it  is  more  transparent.     A  small 

portion  of  the  plant  should  be  placed 
on    the   glass   slip  in    water  with   the 
cover  glass  over  a  tuft  of  the  branches 
near  the  growing  end.     Examined  with 
the  microscope  the  green  chlorophyll  bodies,  which 
form  oval  or  oblong  discs,  are  seen  to  be  very  numer- 
ous.    They  lie  quite  closely  side  by  side  and  form  in 
perfect  rows  along  the  inner  surface  of  the  wall.     One 
peculiar  feature  of  the  arrangement  of  the  chlorophyll 
bodies  is  that  there  are  two  lines,  extending  from  one 
end  of  the  internode  to  the  other  on  opposite  sides, 
where  the  chlorophyll  bodies  are  wanting.     These  are 
known  as  neutral  lines.     They  run  parallel  with  the 
axis  of  the  internode,  or  in   a   more   or  less   spiral 
manner  as  shown  in  fig.  9. 

20.  Cyclosis  in  nitella.— The  chlorophyll  bodies 
are  stationary  on  the   inner  surface  of  the  wall,  but 
if  the  microscope  be  properly  focussed  just  beneath 
this  layer  we  notice   a  rotary  motion  of  particles  in 
the  protoplasm.     There  are  small  granules  and  quite 
large  masses  of  granular  matter  which  glide  slowly 
along  in  one  direction  on  a  given  side  of  the   neutral 
line.     If  now  we  examine  the  protoplasm  on  the  other 
side  of  the  neutral  line,  we  see  that  the  movement  is 

in  the  opposite  direction.      If  we  examine  this  move-  ^  lg',  ' 

Portion  of  plant  nitella. 
ment  at  the  end  of  an  internode  the  particles  are  seen 

to  glide  around  the  end  from  one  side  of  the  neutral  line  to  the  other.  So 
that  when  conditions  are  favorable,  such  as  temperature,  healthy  state  of  the 
plant,  etc.,  this  gliding  of  the  particles  or  apparent  streaming  of  the  proto- 
plasm down  one  side  of  the  "  cell,"  and  back  upon  the  other,  continues  in 
an  uninterrupted  rotation,  or  cyclosis.  There  are  many  nuclei  in  an  internode 
of  nitella,  and  they  move  also. 

21.  Test  for  protoplasm. — If  we  treat  the  plant  with  a  solution  of  iodine 
we  get  the  same  reaction  as  in  the  case  of  spirogyra  and  mucor.     The  proto- 
plasm becomes  yellowish  brown. 

22.  Protoplasm  in  one  of  the  higher  plants. — We  now  wish 
to  examine,  and  test  for,  protoplasm  in  one  of  the  higher  plants. 


IO  PHYSIOLOGY. 

Young  or  growing  parts  of  any  one  of  various  plants — the  petioles 
of  young  leaves,  or  young  stems  of  growing  plants — are  suitable 
for  study.  Tissue  from  the  pith  of  corn  (Zea  mays)  in  young 

shoots  just  back  of  the 
growing  point  or  quite 
near  the  joints  of  older  but 
growing  corn  stalks  fur- 
Fig  9  nishes  excellent  material. 

Cyclosis  in  nitella.  If  we    should  place  part 

of  the  stem  of  this  plant  under  the  microscope  we  should  find 
it  too  opaque  for  observation  of  the  interior  of  the  cells.  This 
is  one  striking  difference  which  we  note  as  we  pass  from  the  low 
and  simple  plants  to  the  higher  and  more  complex  ones  ;  not 
only  in  general  is  there  an  increase  of  size,  but  also  in  general 
an  increase  in  thickness  of  the  parts.  The  cells,  instead  of  lying 
end  to  end  or  side  by  side,  are  massed  together  so  that  the  parts 
are  quite  opaque.  In  order  to  study  the  interior  of  the  plant 
we  have  selected  it  must  be  cut  into  such  thin  layers  that  the 
light  will  pass  readily  through  them. 

For  this  purpose  we  section  the  tissue  selected  by  making  with 
a  razor,  or  other  very  sharp  knife,  very  thin  slices  of  it.  These 
are  mounted  in  water  in  the  usual  way  for  microscopic  study.  In 
this  section  we  notice  that  the  cells  are  polygonal  in  form. 
This  is  brought  about  by  mutual  pressure  of  all  the  cells.  The 
granular  protoplasm  is  seen  to  form  a  layer  just  inside  the  wall, 
which  is  connected  with  the  nuclear  layer  by  radiating  strands 
of  the  same  substance.  The  nucleus  does  not  always  lie  at  the 
middle  of  the  cell,  but  often  is  near  one  side.  If  we  now  apply 
an  alcohol  solution  of  iodine  the  characteristic  yellowish-brown 
color  appears.  So  we  conclude  here  also  that  this  substance  is 
identical  with  the  living  matter  in  the  other  very  different  plants 
which  we  have  studied. 

23.  Movement  of  protoplasm  in  the  higher  plants. — Cer- 
tain parts  of  the  higher  plants  are  suitable  objects  for  the  study 
of  the  so-called  streaming  movement  of  protoplasm,  especially 
the  delicate  hairs,  or  thread-like  outgrowths,  such  as  the  silk  of 


PROTOPLASM.  II 

corn,  or  the  delicate  staminal  hairs  of  some  plants,  like  those  of 
the  common  spiderwort,  tradescantia,  or  of  the  tradescantias 
grown  for  ornament  in  greenhouses  and  plant  conservatories. 

Sometimes  even  in  the  living  cells  of  the  corn  plant  which  we 
have  just  studied,  slow  streaming  or  gliding  movements  of  the 
granules  are  seen  along  the  strands  of  protoplasm  where  they 
radiate  from  the  nucleus.  See  note  at  close  of  this  chapter. 

24.  Movement  of  protoplasm  in  cells  of  the  staminal  hair  of 
"  spiderwort." — A  cell  of  one  of  these  hairs  from  a  stamen  of  a 
tradescantia  grown  in  glass  houses  is  shown  in  fig.  10.  The 


Fig.  10. 
Cell  from  stamen  hair  of  tradescantia  showing  movement  of  the  protoplasm. 

nucleus  is  quite  prominent,  and  its  location  in  the  cell  varies  con- 
siderably in  different  cells  and  at  different  times.  There  is  a 
layer  of  protoplasm  all  around  the  nucleus,  and  from  this  the 
strands  of  protoplasm  extend  outward  to  the  wall  layer.  The 
large  spaces  between  the  strands  are,  as  we  have  found  in  other 
cases,  filled  with  the  cell-sap. 

An  entire  stamen,  or  a  portion  of  the  stamen,  having  seveial  hairs  attached, 
should  be  carefully  mounted  in  water.  Care  should  be  taken  that  the  room  be 
not  cold,  and  if  the  weather  is  cold  the  water  in  which  the  preparation  is 
mounted  should  be  warm.  With  these  precautions  there  should  be  little  diffi- 
culty in  observing  the  streaming  movement. 

The  movement  is  detected  by  observing  the  gliding  of  the 
granules.  These  move  down  one  of  the  strands  from  the  nucleus 
along  the  wall  layer,  and  in  towards  the  nucleus  in  another 
strand.  After  a  little  the  direction  of  the  movement  in  any  one 
portion  may  be  reversed. 

25.  Cold  retards  the  movement. — While  the  protoplasm  is 
moving,  if  we  rest  the  glass  slip  on  a  block  of  ice,  the  move- 
ment will  become  slower,  or  will  cease  altogether.  Then  if  we 


12  PHYSIOLOGY. 

warm  the  slip  gently,  the  movement  becomes  normal  again.  We 
may  now  apply  here  the  usual  tests  for  protoplasm.  The  result 
is  the  same  as  in  the  former  cases. 

26.  Protoplasm  occurs  in  the  living  parts  of  all  plants. — 
In  these  plants  representing  such  widely  different  groups,  we  find 
a  substance  which  is  essentially  alike  in  all.     Though  its  arrange- 
ment in  the  cell  or  plant  body  may  differ  in  the  different  plants 
or  in  different  parts  of  the  same  plant,  its  general  appearance 
is  the  same.     Though  in  the  different  plants  it  presents,  while 
alive,  varying  phenomena,  as  regards  mobility,  yet  when  killed 
and  subjected  to  well  known  reagents  the  reaction  is  in  general 
identical.     Knowing  by  the  experience  of  various  investigators 
that  protoplasm  exhibits  these  reactions  under  given  conditions, 
we  have  demonstrated  to  our  satisfaction  that  we  have  seen  proto 
plasm  in  the   simple  alga,    spirogyra,   in  the  common   mould, 
mucor,  in  the  more  complex  stonewort,  nitella,  and  in  the  cells 
of  tissues  of  the  highest  plants. 

27.  By  this  simple  process  of  induction  of  these  facts  concerning 
this  substance  in  these  different  plants,  we  have  learned  an  im- 
portant method  in  science  study.     Though  these  facts  and  deduc- 
tions are  well  known,  the  repetition  of  the  methods  by  which  they 
are  obtained  on  the  part  of  each  student  helps  to  form  habits  of 
scientific  carefulness  and  patience,  and  trains  the  mind  to  logical 
processes  in  the  search  for  knowledge. 

28.  While  we  have  by  no  means  exhausted  the  study  of  protoplasm,  we  can, 
from  this  study,  draw  certain  conclusions  as  to  its  occurrence  and  appearance 
in  plants.  Protoplasm  is  found  in  the  living  and  growing  parts  of  all  plants. 
It  is  a  semi-fluid,  or  slimy,  granular,  substance  ;  in  some  plants,  or  parts  of 
plants,  the  protoplasm  exhibits  a  streaming  or  gliding  movement  of  the  gran- 
ules. It  is  irritable.  In  the  living  condition  it  resists  more  or  less  for  some 
time  the  absorption  of  certain  coloring  substances.  The  water  may  be  with- 
drawn by  glycerine.  The  protoplasm  may  be  killed  by  alcohol.  When 
treated  with  iodine  it  becomes  a  yellowish-brown  color. 

Note.  In  some  plants,  like  elodea  for  example,  it  has  been  found  that 
the  streaming  of  the  protoplasm  is  often  induced  by  some  injury  or  stimu- 
lus, while  in  the  normal  condition  the  protoplasm  does  not  move. 


CHAPTER    II. 
ABSORPTION,  DIFFUSION,  OSMOSE. 

29.  We   may    next   endeavor    to   learn   how   plants   absorb 
water  or  nutrient   substances   in  solution.     There   are    several 
very  instructive  experiments,  which   can  be  easily  performed, 
and  here  again  some  of  the  lower  plants  will  be  found  useful. 

30.  Osmose  in  spirogyra. — Let  us  mount  a  few  threads  of 
this  plant  in  water  for  microscopic  examination,  and  then  draw 
under  the  cover  glass  a  five  per  cent  solution  of  ordinary  table 
salt  (NaCl)  with  the  aid  of  filter  paper.     We  shall  soon  see 
that  the  result  is  similar  to  that  which  was  obtained  when  glycer- 
ine was  used  to  extract  the  water  from  the  cell-sap,  and  to  con- 
tract the  protoplasmic  membrane  from  the  cell  wall.     But  the 
process  goes  on  evenly  and  the  plant  is  not  injured.     The  proto- 
plasmic layer  contracts  slowly  from  the  cell  wall,  and  the  move- 
ment of  the  membrane  can  be  watched  by  looking  through  the 
microscope.     The  membrane  contracts  in  such  a  way  that  all 
the  contents  of  the  cell  are  finally  collected  into  a  rounded  or 
oval  mass  which  occupies  the  center  of  the  cell. 

If  we  now  add  fresh  water  and  draw  off  the  salt  solution, 
we  can  see  the  protoplasmic  membrane  expand  again,  or  move 
out  in  all  directions,  and  occupy  its  former  position  against  the 
inner  surface  of  the  cell  wall.  This  would  indicate  that  there  is 
some  pressure  from  within  while  this  process  of  absorption  is 
going  on,  which  causes  the  membrane  to  move  out  against  the 
cell  wall. 

The  salt  solution  draws  water  from  the  cell-sap.  There 
is  thus  a  tendency  to  form  a  vacuum  in  the  cell,  and  the 
pressure  on  the  outside  of  the  protoplasmic  membrane  causes  it 

13 


PHYSIOLOGY. 


to  move  toward  the  center  of  the  cell.  When  the  salt  solution 
is  removed  and  the  thread  of  spirogyra  is  again  bathed  with 
water,  the  movement  of  the  water  is  inward  in 
the  cell.  This  would  suggest  that  there  is  some 
substance  dissolved  in  the  cell-sap  which  does  not 
readily  filter  out  through  the  membrane,  but  draws 
on  the  water  outside.  It  is  this  which  produces 
the  pressure  from  within  and  crowds  the  mem- 
brane out  against  the  cell  wall  again. 


Fig.  ii. 

Spirogyra  before 
placing  in  salt  solu- 
tion. 


Fig.  13. 

Spirogyra    from    salt 
solution  into  water. 


Fig.  12. 
Spirogyra  in  5^  salt  solution. 


31.   Turgescence.— Were  it  not  for  the  resistance  which  the 
cell  wall  offers  to  the  pressure  from  within,  the  delicate  proto- 


ABSORPTION,  DIFFUSION,   OSMOSE. 


plasmic  membrane  would  stretch  to  such  an  extent  that  it  would 
be  ruptured,  and  the  protoplasm  therefore  would  be  killed.  If 
we  examine  the  cells  at  the  ends  of  the 
threads  of  spirogyra  we  shall  see  in  most 
cases  that  the  cell  wall  at  the  free  end  is 
arched  outward. 
This  is  brought 
about  by  the  press- 


Fig.  16. 

From  salt  solution  placed  in  water. 
Figs.  14-16. — Osmosis  in  threads  of  mucor. 


Fig.  14. 

frefore  treatment  with  salt 
solution. 

ure  from  within 
upon  the  proto-  After  Jj^ 
plasmic  m  e  m  - 
brane  which  itself  presses  against 
the  cell  wall,  and  causes  it  to 
arch  outward.  This  is  beauti- 
fully shown  in  the  case  of  threads 
which  are  recently  broken.  The  cell  wall  is  therefore  elastic; 
it  yields  to  a  certain  extent  to  the  .pressure  from  within,  but  a 
point  is  soon  reached  beyond  which  it  will  not  stretch,  and  an 
equilibrium  then  exists  between  the  pressure  from  within  on  the 
protoplasmic  membrane,  and  the  pressure  from  without  by  the 
elastic  cell  wall.  This  state  of  equilibrium  in  a  cell  is  turges 
cence,  or  such  a  cell  is  said  to  be  turgescent,  or  turgid. 

32.  Experiment  with  beet  in  salt  and  sugar  solutions. — 
We  may  now  test  the  effect  of  a  five  per  cent  salt  solution  on  a 
portion  of  the  tissues  of  a  beet  or  carrot.  Let  us  cut  several 
slices  of  equal  size  and  about  $mm  in  thickness.  Immerse  a 
few  slices  in  water,  a  few  in  a  five  per  cent  salt  solution  and  a 
few  in  a  strong  sugar  solution.  It  should  be  first  noted  that  all 
the  slices  are  quite  rigid  when  an  attempt  is  made  to  bend  them 
between  the  fingers.  In  the  course  of  one  or  two  hours  or  less, 


i6 


PHYSIOLOGY. 


if  we  examine  the  slices  we  shall  find  that  those  in  water  remain, 
as  at  first,  quite  rigid,  while  those  in  the  salt  and  sugar  solutions 
are  more  or  less  flaccid  or  limp,  and  readily  bend  by  pies- 


Fig.  17.  Fig.  18.  Fig.  19. 

Before  treatment  with  salt    After    treatment    with    salt     From  salt  solution  into  water 
solution.  solution.  again. 

Figs.  17-19. — Osmosis  in  cells  of  Indian  corn. 

sure  between  the  fingers,  the  specimens  in  the  salt  solution, 
perhaps,  being  more  flaccid  than  those  in  the  sugar  solution. 
The  salt  solution,  we  judge  after  our  experiment  with  spirogyra, 


Fig.  20.  Fig.  21.  Fig.  22. 

Rigid  condition  of  fresh  beet    Limp  condition  after  lying  in     Rigid  again  after  Ivine  ac-ai" 
section.  salt  solution.  in  water.      ' 

Figs.  20-22.— Turgor  and  osmosis  in  slices  of  beet. 

withdraws  some  of  the  water  from  the  cell-sap,  the  cells  thus 
losing  their  turgidity  and  the  tissues  becoming  limp  or  flaccid 
from  the  loss  of  water. 


ABSORPTION,  DIFFUSION,   OSMOSE.  I? 

33.  Let  us  now  remove  some  of  the  slices  of  the  beet  from 
the  sugar  and  salt  solutions,  wash  them  with  water  and  then 
immerse  them  in  fresh  water.  In  the  course  of  thirty  minutes 
to  one  hour,  if  we  examine  them  again,  we  find  that  they  have 
regained,  partly  or  completely,  their  rigidity.  Here  again  we 
infer  from  the  former  experiment  with  spirogyra  that  the  sub- 
stances in  the  cell-sap  now  draw  water  inward  ;  that  is,  the 
diffusion  current  is  inward  through  the  cell  walls  and  the  proto- 
plasmic membrane,  and  the  tissue  becomes  turgid  again. 

34.  Osmose  in  the  cells  of  the  beet. — We  should  now  make  a  section  of  the 
fresh  tissue  of  a  red  colored  beet  for  examination  with  the  microscope,  and 
treat  this  section  with  the  salt  solution.  Here  we  can  see  that  the  effect  of  the 
salt  solution  is  to  draw  water  out  of  the  cell,  so  that  the  protoplasmic  mem- 


Fig.  23.  Fig.  24.  Fig.  25. 

Before    treatment    with    salt     After    treatment     with     salt          Later  stage  of  the  same. 

solution.  solution. 

Figs.  23-25. — Cells  from  beet  treated  with  salt  solution  to  show  osmosis  and  movement  of 
the  protoplasmic  membrane. 

brane  can  be  seen  to  move  inward  from  the  cell  wall  just  as  was  observed  in 
the  case  of  spirogyra.*  Now  treating  the  section  with  water  and  removing 
the  salt  solution,  the  diffusion  current  is  in  the  opposite  direction,  that  is  in- 


*  We  should  note  that  the  coloring  matter  of  the  beet  reside?  in  the  cell- 
sap.  It  is  in  these  colored  cells  that  we  can  best  see  the  movement  take 
place,  since  the  red  color  serves  to  differentiate  well  the  moving  mass  from  the 
cell  wall.  The  protoplasmic  membrane  at  several  points  usually  clings  tena- 
ciously so  that  at  several  places  the  membrane  is  arched  strongly  away  from 
the  cell  wall  as  shown  in  fig.  24.  While  water  is  removed  from  the  cell-sap, 
we  note  that  the  coloring  matter  does  not  escape  through  the  protoplasmic 
membrane. 


IS  PHYSIOLOGY. 

ward  through  the  protoplasmic  membrane,  so  that  the  latter  is  pressed  outward 
until  it  comes  in  contact  with  the  cell  wall  again,  which  by  its  elasticity  soon 
resists  the  pressure  and  the  cells  again  become  turgid. 

35.  The  coloring  matter  in  the  cell  sap  does  not  readily  escape  from  the 
living  protoplasm  of  the  beet. — The  red  coloring  matter,  as  seen  in  the  sec- 
tion under  the  microscope,  does  not  escape  from  the  cell-sap  through  the  pro- 
toplasmic membrane .     When  the  slices  are  placed  in  water,  the  water  is  not 
colored  thereby.     The  same  is  true  when  the  slices  are  placed  in  the  salt  or 
sugar  solutions.    Although  water  is  withdrawn  from  the  cell-sap,  this  coloring 
substance  does  not  escape,  or  if  it  does  it  escapes  slowly  and  after  a  consider- 
able time. 

36.  The  coloring  matter  escapes  from  dead  protoplasm. — If,  however,  we 
heat  the  water  containing  a  slice  of  beet  up  to  a  point  which  is  sufficient  to 
kill  the  protoplasm,  the  red  coloring  matter  in  the  cell-sap  filters  out  through 
the  protoplasmic  membrane  and  colors  the  water.     If  we  heat  a  preparation 
made  for  study  under  the  microscope  up  to  the  thermal  death  point  we  can 
see  here  that  the  red  coloring  matter  escapes  through  the  membrane  into  the 
water  outside.     This  teaches  that    certain  substances   cannot   readily   filter 
through  4he  living  membrane  of  protoplasm,  but  that  they  can  filter  through 
when  the  protoplasm  is  dead.     A  very  important  condition,  then,  for  the  suc- 
cessful operation  of  some  of  the  physical  processes  connected  with  absorption 
in  plants  is  that  the  protoplasm  should  be  in  a  living  condition. 

37.  Osmose  experiments  with  leaves. — We  may  next  take  the  leaves  of 
certain  plants  like  the  geranium,  coleus  or  other  plant,  and  place  them  in 
shallow  vessels  containing  water,  salt,  and  sugar  solutions  respectively.     The 
leaves  should  be  immersed,  but  the  petioles  should  project  out  of  the  water  or 
solutions.     Seedlings  of  corn  or  beans,  especially  the  latter,   may  also  be 
placed  in  these  solutions,  so  that  the  leafy  ends  are  immersed.     After  one  or 
two  hours  an   examination  shows  that  the  specimens  in  the  water  are  still 
turgid.         But  if  we  lift  a  leaf  or  a  bean  plant  from  the  salt  or  sugar  solution, 
we   find   that   it   is   flaccid   and   limp.     The   blade,  or   lamina,  of  the  leaf 
droops  as  if  wilted,  though  it  is  still  wet.     The  bean  seedling  also  is  flaccid, 
the  succulent  stem  bending  nearly  double  as  the  lower  part  of  the  stem  is  held 
upright.     This  loss  of  turgidity  is  brought  about  by  the  loss  of  water  from  the 
tissues,  and  judging  from  the  experiments  on  spirogyra  and  the  beet,  we  con- 
clude that  the  loss  of  turgidity  is  caused  by  the  withdrawal  of  some  of  the 
water  from  the  cell-sap  by  the  strong  salt  solution. 

38.  Now  if  we  wash  carefully  these  leaves  and  seedlings,  which  have  been 
in  the  salt  and  sugar  solutions,  with  water,  and  then   immerse  them  in  fresh 
water  for  a  few  hours,  they  will  regain  their  turgidity.    Here  again  we  are  led 
to  infer  that  the  diffusion  current  is  now  inward  through  the  protoplasmic 
membranes  of  all  the  living  cells  of  the  leaf,  and  that  the  resulting  turgidity 
of  the  individual  cells  causes  the  turgidity  of  the  leaf  or  stem. 


ABSORPTION,  DIFFUSION,  OSMOSE. 


39.  Absorption  by  root  hairs. — If  we  examine  seedlings, 
which  have  been  grown  in  a  germinator  or  in  the  folds  of  paper 
or  cloths  so  that  the  roots  will  be  free  from  particles  of  soil,  we 
see  near  the  growing  point  of  the  roots  that  the  surface  is 
covered  with  numerous  slender,  delicate,  thread- 
like bodies,  the  root  hairs.  Let  us  place  a  por- 
tion of  a  small  root  containing  some  of  these 
root  hairs  in  water  on  a  glass  slip,  and  prepare  it 
for  examination  with  the  microscope.  We  see 
that  each  thread,  or  root  hair,  is  a  continuous 
tube,  or  in  other  words  it  is  a  single  cell  which 
has  become  very  much  elongated.  The  proto- 
plasmic membrane  lines  the  wall,  and  strands  of 
protoplasm  extend  across  at  irregular  intervals,  the 
interspaces  being  occupied  by  the  cell -sap. 

We   should   now  draw   under  the  cover  glass 
some  of  the   five   per   cent   salt  solution.       The 
protoplasmic  membrane  moves  away  from  the  cell 
wall  at  certain  points,  showing  that  plasmolysis  is 
taking  place,  that  is,  the  diffusion  current  is  out- 
ward so  that  the  cell-sap  loses  some  of  its  water, 
and   the   pressure   from   the   outside   moves   the 
membrane  inward.     We  should  not  allow  the  salt 
solution  to  work  on  the  root  hairs  long.     It  should 
be  very  soon  removed  by  drawing  in  fresh  water 
before    the    protoplasmic    membrane   has    been 
broken  at  intervals,  as  is 
apt  to  be  the  case  by  the 
strong  diffusion  current 
and     the     consequent 
strong    pressure    from 


Fig.  27. 

Root  hair  of  corn 

Fig.  26.  before    and    after 

Without.      The  membrane   Seedling  of  radish,  showing  root  treatment    with 


hairs. 


salt  solution. 


of  protoplasm  now  moves 

outward  as  the  diffusion  current  is  inward,  and  soon  regains  its 
former  position  next  the  inner  side  of  the  cell  wall.  The 
root  hairs  then,  like  other  parts  of  the  plant  which  we  have 


20 


PHYSIOLOGY. 


investigated,    have  the  power  of  taking  up  water  under  press- 
ure. 

40.  Cell-sap  a  solution  of  certain  substances  — From  these  experiments  we 
are  led  to  believe  that  certain  substances  reside  in  the  cell-sap  of  plants,  which 
behave  very  much  like   the   salt  solution  when   separated  from  water  by  the 
protoplasmic  membrane.      Let  us  attempt  to  interpret  these  phenomena  by 
recourse  to  diffusion  experiments,  where  an  animal  membrane  separates  two 
liquids  of  different  concentration. 

41.  An  artificial  cell  to  illustrate  turgor. — Fill  a  small  wide-mouthed 
vial  with  a  very  strong  sugar  solution.     Over  the  mouth  tie  firmly  a  piece 
of  bladder  membrane.     Be  certain  that  as  the  membrane  is  tied  over  the 
open  end  of  the  vial,  the  sugar  solution  fills  it  in  order  to  keep  out  air- 


FlG.  28.  Puncturing 
a  make-believe  cell 
after  it  has  been 
lying  in  water. 


FIG.   ap.      Same   as  Fig.    28 
after  needle  is  removed. 


bubbles.  Sink  the  vial  in  a  vessel  of  fresh  water  and  leave  it  there  for  twenty- 
four  hours.  Remove  the  vial  and  note  that  the  membrane  is  arched  out- 
ward. Thrust  a  sharp  needle  through  the  membrane  when  it  is  arched 
outward,  and  quickly  pull  it  out.  The  liquid  spurts  out  because  of  the 
inside  pressure. 

42.  Diffusion  through  an  animal  membrane. — For  this  experiment  we 
may  use  a  thistle  tube,  across  the  larger  end  of  which  should  be  stretched  and 
tied  tightly  a  piece  of  a  bladder  membrane.  A  strong  sugar  solution  (three 
parts  sugar  to  one  part  water)  is  now  placed  in  the  tube  so  that  the  bulb  is 


ABSORPTION,    DIFFUSION,    OSMOSE.  21 

filled  and  the  liquid  extends  part  way  in  the  neck  of  the  tube.  This  is  im- 
mersed in  water  within  a  wide-mouth  bottle,  the  neck  of  the  tube  being  sup- 
ported in  a  perforated  cork  in  such  a  way  that  the  sugar  solution  in  the  tube  is 
on  a  level  with  the  water  in  the  bottle  or  jar.  In  a  short  while  the  liquid 
begins  to  rise  in  the  thistle  tube,  in  the  course  of  several  hours  having  risen 
several  centimeters.  The  diffusion  current  is  thus  stronger  through  the  mem- 
brane in  the  direction  of  the  sugar  solution,  so  that  this  gains  more  water  than 
it  loses. 

We  have  here  two  liquids  separated  by  an  animal  membrane,  water  on 
the  one  hand  which  diffuses  readily  through  the  membrane,  while  on  the  other 
is  a  solution  of  sugar  which  diffuses  through  the  animal  membrane  with  diffi- 
culty. The  water,  therefore,  not  containing  any  solvent,  according  to  a 
general  law  which  has  been  found  to  obtain  in  such  cases,  diffuses  more 
readily  through  the  membrane  into  the  sugar  solution,  which  thus  increases  in 
v6lume,  and  also  becomes  more  dilute.  The  bladder  membrane  is  what  is 
sometimes  called  a  diffusion  membrane,  since  the  diffusion  currents  travel 
through  it. 

43.  In  this  experiment  then  the  bulk  of  the  sugar  solution  is  increased,  and 
the  liquid  rises  in  the  tube  by  this  pressure  above  the  level  of  the  water  in  the 
jar  outside  of  the  thistle  tube.     The  diffusion  of  liquids  through  a  membrane 
Is  osmosis. 

44.  Importance  of  these  physical  processes  in  plants. — Now  if  we  recur 
to  our  experiment  with  spirogyra  we  find  that  exactly  the  same  processes  take 
place.     The  protoplasmic  membrane  is  the  diffusion  membrane,  through  which 
the  diffusion  takes  place.      The  salt  solution  which  is  first  used  to  bathe  the 
threads  of  the  plant  is  a  stronger  solution  than  that  of  the  cell-sap  within  the 
cell.     Water   therefore    is   drawn    out  of  the  cell-sap,  but  the  substances  in 
solution  in  the  cell-sap  do  not  readily  move  out.     As  the  bulk  of  the  cell-sap 
diminishes  the   pressure  from  the  outside  pushes  the  protoplasmic  membrane 
away  from   the  wall.     Now  when  we  remove  the  salt  solution  and  bathe 
the   thread  with  water  again,  the  cell-sap,  being   a    solution   of  certain   sub- 
stances, diffuses  with  more  difficulty  than  the  water,  and  the  diffusion  current 
is  inward,  while  the  protoplasmic  membrane  moves  out  against  the  cell  wall, 
and  turgidity  again  results.     Also  in  the  experiments  with  salt  and  sugar  solu- 
tions on  the  leaves  of  geranium,  on  the  leaves  and  stems  of  the  seedlings,  on 
the  tissues  and  cells  of  the  beet  and  carrot,  and  on  the  root  hairs  of  the  seed- 
lings, the  same  processes  take  place. 

These  experiments  not  only  teach  us  that  in  the  protoplasmic  membrane,  the 
cell  wall,  and  the  cell-sap  of  plants  do  we  have  structures  which  are  capable  of 
performing  these  physical  processes,  but  they  also  show  that  these  processes  are 
of  the  utmost  importance  to  the  plant ;  not  only  in  giving  the  plant  the  power 
to  take  up  solutions  of  nutriment  from  the  soil,  but  they  serve  also  other  pur- 
poses, as  we  shall  see  later. 


CHAPTER   III. 

HOW    PLANTS    OBTAIN   WATER. 

In  connection  with  the  study  of  the  means  of  absorption  from  the  soil 
or  water  by  plants,  it  will  be  found  convenient  to  observe  carefully  the 
various  forms  of  the  plant.  Without  going  into  detail  here,  the  suggestion 
is  made  that  simple  thread  forms  like  spirogyra,  oedogonium,  and  vau- 
cheria;  expanded  masses  of  cells  as  are  found  in  the  thalloid  liverworts, 
the  duckweed,  etc.,  be  compared  with  those  liverworts,  and  with  the  mosses, 
where  leaf-like  expansions  of  a  central  axis  have  been  differentiated.  We 
should  then  note  how  this  differentiation,  from  the  physiological  stand- 
point, has  been  carried  farther  in  the  higher  land  plants. 

45.  Absorption  by  Algae  and  Fungi. — In  the  simpler  forms  of  plant  life, 
as  in  spirogyra  and  many  of  the  algae  and  fungi,  the  plant  body  is  not  dif- 
ferentiated into  parts.*  In  many  other  cases  the  only  differentiation  is 
between  the  growing  part  and  the  fruiting  part.  In  the  algae  and  fungi 
there  is  no  differentiation  into  stem  and  leaf,  though  there  is  an  approach 
to  it  in  some  of  the  higher  forms.  Where  this  simple  plant  body  is  flat- 
tened, as  in  the  sea-wrack,  or  ulva,  it  is  a  frond.  The  Latin  word  for 
frond  is  thallus,  and  this  name  is  applied  to  the  plant  body  of  all  the  lower 
plants,  the  algae  and  fungi.  The  algae  and  fungi  together  are  sometimes 
called  the  thallophytes,  or  thallus  plants.  The  word  thallus  is  also  some- 
times applied  to  the  flattened  body  of  the  liverworts.  In  the  foliose  liver- 
worts and  mosses  there  is  an  axis  with  leaf-like  expansions.  These  are 
believed  by  some  to  represent  true  stems  and  leaves,  by  others  to  represent 
a  flattened  thallus  in  which  the  margins  are  deeply  and  regularly  divided,  or 
in  which  the  expansion  has  only  taken  place  at  regular  intervals. 

In  nearly  all  of  the  algae  the  plant  body  is  submerged  in  water.     In  these 

*  See  Chapter  38  for  organization  of  members  of  the  plant  body. 

22 


HOW  PLANTS   OBTAIN    WATER. 


cases  absorption  takes  place  through  all  portions  of  the  surface  in  contact 
with  the  water,  as  in  spirogyra,  vaucheria,  and  all  of  the  larger  seaweeds. 
Comparatively  few  of  the  algae  grow  on  the  surfaces  of  rocks  or  trees.  IE 
these  examples  it  is  likely  that  at  times  only  portions  of  the  plant  body 
serve  in  the  process  of  absorption  of  water  from  the  substratum.  A  few  of 
the  algae  are  parasitic,  living  in  the  tissues  of  higher  plants,  where  they  are 
surrounded  by  the  water  or  liquids  within  the  host.  Absorption  takes 
place  in  the  same  way  in  many  of  the  fungi.  The  aquatic  fungi  are  im- 
mersed in  water.  In  other  forms,  like  mucor,  a  portion  of  the  mycelium 
is  within  the  substratum,  and  being  bathed  by  the  water  or  watery  solu- 
tions absorbs  the  same,  while  the  fruiting  portion  and  the  aerial  mycelium 
obtain  their  water  and  food  solutions  from  the  mycelium  in  the  substratum. 
In  higher  fungi,  like  the  mushrooms,  the  mycelium  within  the  ground  or 
decaying  wood  absorbs  the  water  necessary  for  the  fruiting  portion;  while 
in  the  case  of  the  parasitic  fungi  the  mycelium  lies  in  the  water  or  liquid 
within  the  host. 

46.  Absorption  by  liverworts.  —  In  many  of  the  plants  termed  liverworts 
the  vegetative  part  of  the  plant  is  a  thin,  flattened,  more  or  less  elongated 
green  body  know  as  a  thallus. 

Riccia.  —  One  of  these,  belonging  to  the  genus  riccia,  is  shown  in  fig.  30. 
Its  shape  is  somewhat  like  that 
of  a  minute  ribbon  which  is 
forked  at  intervals  in  a  dichot- 
omous  manner,  the  character- 
istic kind  of  branching  found,  in 
these  thalloid  liverworts.  This 
riccia  (known  as  R.  lutescens) 
occurs  on  damp  soil;  long, 
slender,  hair-like  processes  grow 
out  from  the  under  surface  of 
the  thallus  which  resemble  root 
hairs  and  serve  the  same  pur- 
pose in  the  processes  of  absorp- 
tion. Another  species  of  riccia 
(R.  crystallina)  is  shown  in  fig. 
252.  This  plant  is  quite  circular  in  outline  and  occurs  on  muddy  flats. 
Some  species  float  on  the  water. 


FiR.  30. 
Thallus  of  Riccia  lutescens. 


47.  Marchantia.  —  One  of  the  larger  and  coarser  liverworts  is 
figured  at  31.  This  is  a  very  common  liverwort,  growing  in 
very  damp  and  muddy  places  and  also  along  the  margins  of 
streams,  on  the  mud  or  upon  the  surfaces  of  rocks  which  are 


24  PHYSIOLOGY. 

bathed  with  the  water.  This  is  known  as  Marchantia  poly- 
morpha.  If  we  examine  the  under  surface  of  the  marchantia 
we  see  numerous  hair-like  processes  which  attach  the  plant  to 
the  soil.  Under  the  microscope  we  see  that  some  of  these  are 
similar  to  the  root  hairs  of  the  seedlings  which  we  have  been 
studying,  and  they  serve  the  purpose  of  absorption.  Since,  how- 
ever, there  are  no  roots  on  the  marchantia  plant,  these  hair-like 


Fig.  31. 

Marchantia  plant  with  cupules  and  gemmae;  rhizoids  below. 


outgrowths  are  usually  termed  here  rhizoids.  In  marchantia  they 
are  of  two  kinds,  one  kind  the  simple  ones  with  smooth  walls, 
and  the  other  kind  in  which  the  inner  surfaces  of  the  walls  are 
roughened  by  processes  which  extend  inward  in  the  form  of  irreg- 
ular tooth-like  points.  Besides  the  hairs  on  the  under  side  of 
the  thallus  we  note  especially  near  the  growing  end  that  there  are 
two  rows  of  leaf-like  scales,  those  at  the  end  of  the  thallus  curv- 
ing up  over  the  growing  end,  thus  serving  to  protect  the  delicate 
tissues  at  the  growing  point. 


HOW  PLANTS   OBTAIN    WATER. 


48.  Frullania.— In  fig.  32  is  shown  another  liverwort,  which 
differs  greatly  in  form  from  the  ones  we  have 
just  been  studying  in  that  there  is  a  well-defined 
axis  with  lateral  leaf-like  outgrowths.  Such  liver- 
worts are  called  foliose  liverworts.  Besides  these 
two  quite  prominent  rows  of  leaves  there  is  a 
third  row  of  poorly  developed  leaves  on  the  under 

surface.  Also 
from  the 
under  surface 
of  the  axis 
we  see  here 
and  there 
slender  out- 
Fig-  34-  growths,  the 

Under    side, 

showing     forked  rhlZOlaS, 
under      row     of        ,  , 

leaves  and  lobes  t    h  T  O  U  g  h 
of  lateral  leaves.          .  . 

which   much 


Fig.  32. 

Portion  of  plant  of 
Frullania,  a  foliose 
liverwort. 


Fig.  33- 

Portion  of  same 
more  highly  magni- 
fied, showing  over- 
lapping leaves. 


of  the  water  is  absorbed. 

49.  Absorption  by  the  mosses. — Among  the  mosses,  which  are 
usually  common  in  moist  and  shaded 
situations,  examples  are  abundant 
which  are  suitable  for  the  study  of 
the  organs  of  absorption.  If  we  take 
for  example  a  plant  of  mnium 
(M.  affine),  which  is  illustrated  in  fig. 
36,  we  note  that  it  consists  of  a  slender 


Fig.  35- 
Foliose  liverwort  (Vxtzzania)  showing  dichotomous  branching  and  overlapping  leaves. 

axis  with  thin  flat,  green,  leaf-like  expansions.     Examining  with 


26  PHYS1OLOG  Y. 

the  microscope  the  lower  end  of  the  axis,  which  is  attached  to 

the  substratum,  there  are  seen  numerous  brown-colored  threads 

more  or  less  branched. 

50.  Absorption  by  the  higher  aquatic  plants.  —  Examples  of 

the  water  plants  which  are  entirely  submerged  in  water  are  the 
water-crowfoots,  some  of  the  pond- 
weeds,  elodea  or  water-weeds,  the  tape- 
grass,  vallisneria,  etc.  In  these  plants 
all  parts  of  the  body  being  submerged, 
they  absorb  water  with  which  they  are 
in  contact.  In  other  aquatic  plants,  like 
the  water-lilies,  some  of  the  pond- 
weeds,  the  duck-meats,  etc.,  are  only 
partially  submerged  in  the  water;  the 
upper  surface  of  the  leaf  or  of  the  leaf- 
like  expansion  being  exposed  to  the  air, 
while  the  under  surface  lies  in  close 
contact  with  the  water,  and  the  stems 
and  the  petioles  of  the  leaves  are  also 
immersed  in  water.  In  these  plants 
absorption  takes  place  through  those 
parts  in  contact  with  the  water. 

51.  Absorption  by  the  duck-meats. 
—These  plants  are  very  curious  ex- 
amples of  the  higher  plants. 

Lemna.  —  One  of  these  is  illustrated  in  fig. 
37.  This  is  the  common  duckweed,  Lemna 
trisidca.  It  is  very  peculiar  in  form  and  in 
its  mode  of  growth.  Each  one  of  the  lateral 
leaf-like  expansions  extends  outwards  by  the 

36.  elongation  of  the  basal  part,  which  becomes 

Female  plant  (gametophyte)   ,  ,     ,       ,  -.T      .  , 

of   a   moss  (mnium),   showing  long  and  slender.     ISext,  two  new  lateral  ex- 


Pansi°ns  are  formed  °n  these  } 
archegonia.  from  near  the  base,  and  thus  the  plant  con- 

tinues to  extend.  The  plant  occurs  in  ponds  and  ditches  and  is  sometimes 
very  common  and  abundant.  It  floats  on  the  surface  of  the  water.  While 
the  flattened  part  of  the  plant  resembles  a  leaf,  it  is  really  the  stem,  no 
leaves  being  present.  This  expanded  green  body  is  usually  termed  a 


HOW  PLANTS   OBTAIN    WATER.  2J 

"frond."     A  single  rootlet  grows  out  from  the  under  side  and  is  destitute 


Fig.  37- 
Fronds  of  the  duckweed  (Lemna  trisculca). 

of  root  hairs.    Absorption  of  water  therefore  takes  place  through  this  rootlet 
and   through  the  under 
side  of  the  "frond." 

52.  Spirodela      poly- 
rhiza. — This    is    a   very 
curious  plant,  closely  re- 
lated to  the  lemna  and 
sometimes  placed  in  the 
same  genus.     It   occurs 

in  similar  situations,  and  pig  3g 

is  very  readily  grown  in     Spirodela  polyrhiza. 

aquaria.     It  reminds  one  of  a  little  insect  as 

seen  in  fig.  38.     There  are  several  rootlets  on 

the  under  side   of  the  frond.      Absorption    of 

water  takes  place  here  in  the  same  way  as  in 

lemna. 

53.  Absorption  in  wolffia. — Perhaps  the  most   curious  of  these  modified 
water  plants  is  the  little  wolffia,  which  contains  the  smallest  specimens  of 
the  flowering  plants.     Two  species  of  this  genus  are  shown  in  figs.  39-41. 
The  plant  body  is  reduced  to  nothing  but  a  rounded  or  oval  green  body, 
which  represents  the  stem.     No  leaves  or  roots  are  present.     The  plants 
multiply  by  "  proliferation,"  the  new  fronds  growing  out  from  a  depression 
on  the  under  side  of  one  end.     Absorption  takes  place  through  the  surface 
in  contact  with  the  water. 

54.  Absorption  by  land  plants.— Water  cultures. — In  connec- 
tion with  our  inquiry  as  to  how  land  plants  obtain  their  water,  it 


28  PHYSIOLOGY. 

will  be  convenient  to  prepare  some  water  cultures  to  illustrate 
this  and  which  can  also  be  used  later  in  our  study  of  nutrition 
(Chapter  IX). 


Fig.  39-  Fig.  40.  Fig.  41. 

Young  frond  of  wolffia  Young  frond  of  wolffia  Another  species  ot 

growing  out  of  older  one.         separating  trom  older  one.         wolffia..  the  two  frond? 

still  connected. 

Chemical  analysis  shows  that  certain  mineral  substances  are 
common  constituents  of  plants.  By  growing  plants  in  different 
solutions  of  these  various  substances  it  has  been  possible  to  deter- 
mine what  ones  are  necessary  constituents  of  plant  food.  While 
the  proportion  of  the  mineral  elements  which  enter  into  the  com- 
position of  plant  food  may  vary  considerably  within  certain 
limits,  the  concentration  of  the  solutions  should  not  exceed  cer- 
tain limits.  A  very  useful  solution  is  one  recommended  by  Sachs, 
and  is  as  follows: 

55 .  Formula  for  water  cultures  : 

Water , 1000      cc. 

Potassium  nitrate o .  5  gr. 

Sodium  chloride °  •  5  " 

Calcium  sulphate °  •  5  " 

Magnesium  sulphate. 0.5" 

Calcium  phosphate 0.5" 

The  calcium  phosphate  is  only  partly  soluble.  The  solution  which  is  not  in 
use  should  be  kept  in  a  dark  cool  place  to  prevent  the  growth  of  minute  algse. 

56.  Several  different  plants  are  useful  for  experiments  in  water  cultures, 
as  peas,  corn,  beans,  buckwheat,  etc.     The  seeds  of  these  plants  may  be 
germinated,  after  soaking  them  for  several  hours  in  warm  water,  by  placing 


HOW  PLANTS   OBTAIN    WATER. 


29 


them  between  the  folds  of  wet  paper  on  shallow  trays,  or  in  the  folds  of  wet 
cloth.  The  seeds  should  not  be  kept  immersed  in  water  after  they  have 
imbibed  enough  to  thoroughly  soak  and  swell  them.  At  the  same  time 
that  the  seeds  are  pla:ed  in  damp  paper  or  cloth  for  germination,  one  lot  of 
the  soaked  seeds  should  be  planted  in  good  soil  and  kept  under  the  same 
temperature  conditions,  for  control.  When  the  plants  have  germinated 
one  series  should  be  grown  in  distilled  water,  which  possesses  no  plant  food; 
another  in  the  nutrient  solution,  and  still  another  in  the  nutrient  solution  to 
which  has  been  added  a  few  drops  of  a  solution  of  iron  chloride  or  ferrous 
sulphate.  There  would  then  be  four  series  of  cultures  which  should  be 
carried  out  with  the  same  kind  of  seed  in  each  series  so  that  the  compari- 
sons can  be  made  on  the  same  species  under  the  different  conditions.  The 
series  should  be  numbered  and  recorded  as  follows: 

No.  I,  soil. 

No.  2,  distilled  water. 

No.  3,  nutrient  solution. 

No.  4,  nutrient  solution  with  a  few  drops  of  iron  solution  added. 

57.  Small  jars  or  wide-mouth  bottles,  or  crockery  jars,  can  be  used  for  the 
water  cultures,  and  the  cultures  are  set  up  as  follows :    A  cork  which  will  just 
ht  in  the  mouth  of  the  bottle,  or  which  can  be  supported  by  pins,  is  perforated 
so  that   there  is  room  to  insert  the  seedling, 

with  the  root  projecting  below  into  the  liquid. 
The  seed  can  be  fastened  in  position  by  insert- 
ing a  pin  through  one  side,  if  it  is  a  large  one, 
or  in  the  case  of  small  seeds  a  cloth  of  a  coarse 
mesh  can  be  tied  over  the  mouth  of  the  bottle 
instead  of  using  the  cork.  After  properly  set- 
ting up  the  experiments  the  cultures  should  be 
arranged  in  a  suitable  place,  and  observed  from 
time  to  time  during  several  weeks.  In  order  to 
obtain  more  satisfactory  results  several  dupli- 
cate series  should  be  set  up  to  guard  against  the 
error  which  might  arise  from  variation  in  indi- 
vidual plants  and  from  accident  Where  there 
are  several  students  in  a  class,  a  single  series 
set  up  by  several  will  act  as  checks  upon  one 
another.  If  glass  jars  are  used  for  the  liquid 
cultures  they  should  be  wrapped  with  black 
paper  or  cloth  to  exclude  the  light  from  the 
liquid,  otherwise  numerous  minute  algae  are  apt  to  grow  and  interfere  with  the 
experiment.  Or  the  jars  may  be  sunk  in  pots  of  earth  to  serve  the  same 
purpose.  If  crockery  jars  are  used  they  will  not  need  covering. 

58.  For  some  time  all  the  plants   grow  equally  well,   until  the  nutriment 
stored  in  the  seed  is  exhausted.     The  numbers  I,  3  and  4,  in  soil  and  nutri- 


Fig.  42. 

Culture  cylinder  to  show  position  of 
corn  seedling  iHansen). 


3O  PHYSIOLOGY. 

ent  solutions,  should  outstrip  number  2,  the  plants  in  the  distilled  water. 
No.  4  in  the  nutrient  solution  with  iron,  having  a  perfect  food,  compares  favor* 
ably  with  the  plants  in  the  soil. 

59.  Plants  take  liquid  food  from  the  soil. — From  these  ex- 
periments then  we  judge  that  such  plants  take  up  the  food  they 
receive  from  the  soil  in  the  form  of  a  liquid,  the  elements  being 
in  solution  in  water. 

If  we  recur  now  to  the  experiments  which  were  performed  with 
the  salt  solution  in  producing  plasmolysis  in  the  cells  of  spirogyra, 
in  the  cells  of  the  beet  or  corn,  and  in  the  root  hairs  of  the  corn 
and  bean  seedlings,  and  the  way  in  which  these  cells  become  tur- 
gid again  when  the  salt  solution  is  removed  and  they  are  again 
bathed  with  water,  we  shall  have  an  explanation  of  the  way  in 
which  plants  take  up  nutrient  solutions  of  food  material  through 
their  roots. 

60.  How  food  solutions  are  carried  into  the  plant. — We  can 


Fig.  43- 
Section  of  corn  root,  showing  root  hairs  formed  from  elongated  epidermal  cells. 

*ee  how  water  and  food   'olutions  are  carried  into  the  plant, 


HOW  PLANTS   OBTAIN    WATER.  31 

and  we  must  next  turn  our  attention  to  the  way  in  which  these 
solutions  are  carried  farther  into  the  plant  We  should  make  a 
section  across  the  root  of  a  seedling  in  the  region  of  the  root 
hairs  and  examine  it  with  the  aid  of  a  microscope.  We  here  see 
that  the  root  hairs  .are  formed  by  the  elongation  of  certain  of  the 
surface  cells  of  the  root.  These  cells  elongate  perpendicularly  to 
the  root,  and  become  $mm  to  6mm  long.  They  are  flexuous  or 
irregular  in  outline  and  cylindrical,  as  shown  in  fig.  43.  The 
end  of  the  hair  next  the  root  fits  in  between  the  adjacent  superfi- 
cial cells  of  the  root  and  joins  closely  to  the  next  deeper  layer  of 
cells.  In  studying  the  section  of  the  young  root  we  see  that  the 
root  is  made  up  of  cells  which  lie  closely  side  by  side,  each  with 
its  wall,  its  protoplasm  and  cell-sap,  the  protoplasmic  membrane 
lying  on  the  inside  of  each  cell  wall. 

61.  In  the  absorption  of  the  watery  solutions  of  plant  food  by  the  root 
hairs,  the  cell-sap,  being  a  more  concentrated  solution,  gains  some  of  the 
former,  since  the  liquid  of  less  concentration  flows  through  the  protoplasmic 
membrane  into  the  more  concentrated  cell-sap,  increasing  the  bulk  of  the  lat- 
ter.    This  makes  the  root  hairs  turgid,  and  at  the  same  time  dilutes  the  cell- 
sap  so  that  the  concentration  is  not  so  great.     The  cells  of  the  root  lying  in- 
side and  close  to  the  base  of  the  root  hairs  have  a  cell-sap  which  is  now  more 
concentrated  than  the  diluted  cell-sap   of  the  hairs,  and  consequently  gain 
some  of  the  food  solutions  from  the  latter,  which  tends  to  lessen  the  content 
of  the  root  hairs  and  also  to  increase  the  concentration  of  the  cell-sap  of  the 
same.     This  makes  it  possible  for  the  root  hairs  to  draw  on  the  soil  for  more 
of  the  food  solutions,  and  thus,  by  a  variation  in  the  concentration  of  the  sub- 
stances in  solution  in  the  cell-sap  of  the  different  cells,  the  food  solutions  are 
carried  along  until  they  reach  the  vascular  bundles,  through  which  the  solu- 
tions are  carried  to  distant  parts  of  the  plant.     Some  believe  that  there  is  a 
rhythmic  action  of  the  elastic  cell  walls  in  these  cells  between  the  root  hairs  and 
the  vascular  bundles.     This  occurs  in  such  a  way  that,  after  the  cell  becomes 
turgid,  it  contracts,  thus  reducing  the  size  of  the  cell  and  forcing  some  of  the 
food  solutions  into  the  adjacent  cells,  when  by  absorption  of  more  food  solu- 
tions, or  water,  the  cell  increases  in  turgidity  again.     This  rhythmic  action  of 
the  cells,  if  it  does  take  place,  would  act  as  a  pump  to  force  the  solutions 
along,  and  would  form  one  of  the  causes  of  root  pressure. 

62.  How  the  root  hairs  get  the  watery  solutions  from  the  soil. — If  we 
examine  the  root  hairs  of  a  number  of  seedlings  which  are  growing  in  the  soil 
under  normal  conditions,  we  shall  see  that  a  large  quantity  of  soil  readily 
clings  to  the  roots.    We  should  note  also  that  unless  the  soil  has  been  recently 
watered  there  is  no  free  water  in  it ;  the  soil  is  only  moist.     We  are  curious 


PHYSIOLOGY. 


to  know  how  plants  can  obtain  water  from  soil  which  is  not  wet.     If  we  at- 
tempt to  wash  off  the  soil  from  the  roots,  being  careful  not  to  break  away  the 


Fig.  44- 
Root  hairs  of  corn  seedling  with  soil  particles  adhering  closely. 

root  hairs,  we  find  that  small  particles  cling  so  tenaciously  to 
the  root  hairs  that  they  are  not  removed.     Placing  a  few  such 

root  hairs  under  the  microscope  it  appears  as  if  here  and  there  the  root  hairs 

were  glued  to  the  minute  soil  particles. 

63.  If  now  we  take  some  of  the  soil  which  is  only  moist,  weigh  it,  and 
then  permit  it  to  become  quite  dry  on  exposure  to  dry  air,  and  weigh  again, 
we   find   that   it   loses   weight   in    drying.       Moisture   has   been   given   oft. 
This  moisture,  it  has  been  found,  forms  an  exceedingly  thin  film  on  the  sur- 
face of  the  minute  soil  particles.     Where  these   soil  particles  lie  closely  to- 
gether, as  they  usually  do  when  massed  together  in  the  pot  or  elsewhere,  this 
thin  film  of  moisture  is  continuous  from  the  surface  of  one  particle  to  that  of  an- 

xher.  Thus  the  soil  particles  which  are  so  closely  attached  to  the  root  hairs 
connect  the  surface  of  the  root  hairs  with  this  film  of  moisture.  As  the  cell- 
sap  of  the  root  hairs  draws  on  the  moisture  film  with  which  they  are  in  con- 
tact, the  tension  of  this  film  is  sufficient  to  draw  moisture  from  distant  parti- 
cles. In  this  way  the  roots  are  supplied  with  water  in  soil  which  is  only 
moist. 

64.  Plants  cannot  remove  all  the  moisture  from  the  soil. — If  we  now  rake 
a  potted  plant,  or  a  pot  containing  a  number  of  seedlings,  place  it  in  a  moder- 
ately dry  room,  and  do  not  add  water  to  the  soil  we  find  in  a  few  days  that 
the    plant   is  wilting.     The    soil    if  examined  will    appear  quite  dry   to  the 
sense   of  touch.     Let   us  weigh  some   of  this   soil,  then  dry  it  by  artificial 


HOW  PLANTS   OBTAIN    WATER.  33 

heat,  and  weigh  again.  It  has  lost  in  weight.  This  has  been  brought  about 
by  driving  off  the  moisture  which  still  remained  in  the  soil  after  the  plant 
began  to  wilt.  This  teaches  that  while  plants  can  obtain  water  from  soil 
which  is  only  moist  or  which  is  even  rather  dry,  they  are  not  able  to  with- 
draw all  the  moisture  from  the  soil. 

65.  "  Root  pressure  "  or  exudation  pressure. — It  is  a  very  com- 
mon thing  to  note,  when  certain  shrubs  or  vines  are  pruned  in 
the  spring,  the  exudation  of  a  watery  fluid  from  the  cut  surfaces. 
In  the  case  of  the  grape  vine  this  has  been  known  to  continue  for 
a  number  of  days,  and  in  some  cases  the  amount  of  liquid,  called 
"sap,"    which   escapes   is   considerable.     In   many   cases   it   is 
directly  traceable  to  the  activity  of  the  roots,  or  root  hairs,  in 
the  absorption  of  water  from  the  soil.     For  this  reason  the  term 
root  pressure  has  been  used  to  denote  the  force  exerted  in  sup- 
plying the  water  from  the  soil.     But  there  are  some  who  object 
to  the  use  of  this  term  "root  pressure."     The  principal  objec- 
tion is  that  the  pressure  which  brings  about  the  phenomenon 
known  as  "bleeding"  by  plants  is  not  present  in  the  roots  alone. 
This  pressure  exists  under  certain  conditions  in  all  parts  of  the 
plant.     The  term  exudation  pressure  has  been  proposed  in  lieu 
of  root  pressure.     It  should  be  remembered  that  the  movement 
of  water  in  the  plant  is  started  by  the  pressure  which  exists  in 
the  root.      If  the  term  "root  pressure"  is  used,  it  should  be 
borne  clearly  in  mind  that  it  does  not  express  the  phenomenon 
exactly  in  all  cases. 

Root  pressure  may  be  measured. — It  is  possible  to  measure 
not  only  the  amount  of  water  which  the  roots  will  raise  in  a 
given  time,  but  also  to  measure  the  force  exerted  by  the  roots 
cruring  root  pressure.  It  has  been  found  that  root  pressure  in 
the  case  of  the  nettle  is  sufficient  to  hold  a  column  of  water  about 
4.5  meters  (15  ft.)  high  (Vines),  while  the  root  pressure  of  the 
vine  (Hales,  1721)  will  hold  a  column  of  water  about  10  meters 
(36.5  ft.)  high,  and  the  birch  (Betula  lutea)  (Clark,  1873)  has  a 
root  pressure  sufficient  to  hold  a  column  of  water  about  25  meters 
(84.7  ft.)  high. 

66.  Experiment  to  demonstrate  root  pressure.  —By  a  very  simple  method 
this  lifting  of  water  by  root  pressure  is  shown.     During  the  summer  season 


34 


PHYSIOLOGY. 


plants  in  the  open  may  be  used  if  it  is  preferred,  but  plants  grown  In  pots 
are  also  very  serviceable,  and  one  may  use  a  potted  begonia  or  balsam,  the 
latter  being  especially  useful.  The  plants  are  usually  convenient  to  obtain 
from  the  greenhouses,  to  illustrate  this  phenomenon. 
The  stem  is  cut  off  rather  close  to  the  soil  and  a  long 
glass  tube  is  attached  to  the  cut  end  of  the  stem,  still 
connected  with  the  roots,  by  the  use  of  rubber  tubing, 
as  shown  in  figure  45,  and  a  very  small  quantity  of  water 
may  be  poured  in  to  moisten  the  cut  end  of  the  stem. 
In  a  few  minutes  the  water  begins  to  rise  in  the  glass 
tube.  In  some  cases  it  rises  quite  rapidly,  so  that  the 
column  of  water  can  readily  be  seen  to  extend  higher 
and  higher  up  in  the  tube  when  observed  at  quite 
short  intervals.  (To  measure  the  force  of  root  pressure 
is  rather  difficult  for  elementary  work.  To  measure  it 
^fl^fefefc  see  Ganong,  Plant  Physiology,  pp.  67,  68,  or  some  other 
book  for  advanced  work. 

jfJt 

^HH  Bp 


Pig.  45. 


67.  In  either  case  where  the  experiment  is 
continued  for  several  days  it  is  noticed  that  the 
column  of  water  or  of  mercury  rises  and  falls  at 
different  times  during  the  same  day,  that  is,  the 
column  stands  at  varying  heights;  or  in  other 
words  the  root  presssure  varies  during  the  day.  With  some  plants 
it  has  been  found  that  the  pressure  is  greatest  at  certain  times 
of  the  day,  or  at  certain  seasons  of  the  year.  Such  variation 
of  root  pressure  exhibits  what  is  termed  a  periodicity,  and  in 
the  case  of  some  plants  there  is  a  daily  periodicity;  while  in 
others  there  is  in  addition  an  annual  periodicity.  With  the 
grape  vine  the  root  pressure  is  greatest  in  the  forenoon,  and 
decreases  from  12-6  P.M.,  while  with  the  sunflower  it  is  greatest 
before  10  A.M.,  when  it  begins  to  decrease.  Temperature  of 
the  soil  is  one  of  the  most  important  external  conditions  affect- 
ing the  activity  of  root  pressure. 


CHAPTER  IV. 

TRANSPIRATION,  OR   THE    LOSS   OF   WATER    BY 
PLANTS. 

68.  We  should  now  inquire  if  all  the  water  which  is  taken  up 
in  excess  of  that  which  actually  suffices  for  turgidity  is  used  in  the 
elaboration  of  new  materials  of  construction.  We  notice  when  a 
leaf  or  shoot  is  cut  away  from  a  plant,  unless  it  is  kept  in  quite 
a  moist  condition,  or  in  a  damp,  cool  place,  that  it  becomes  flac- 
cid, and  droops.  It  wilts,  as  we  say.  The  leaves  and  shoot  lose 
their  turgidity.  This  fact  suggests  that  there  has  been  a  loss  of 
water  from  the  shoot  or  leaf.  It  can  be  readily  seen  that  this 
loss  is  not  in  the  form  of  drops  of  water  which  issue  from  the  cut 
end  of  the  shoot  or  petiole.  What  then  becomes  of  the  water  in 
the  cut  leaf  or  shoot  ? 


Pig.  46. 
To  show  loss  of  water  from  leaves,  the  leaves  just  covered. 

69.  Loss  of  water  from  excised  leaves. — Let  us  take  a  handful 
of  fresh,  green,  rather  succulent  leaves,  which  are  free  from 

35 


30  PHYSIOLOGY. 

water  on  the  surface,  and  place  them  under  a  glass  bell  jar,  which 
is  tightly  closed  below  but  which  contains  no  water.  Now  place 
this  in  a  brightly  lighted  window,  or  in  sunlight.  In  the  course 
of  fifteen  to  thirty  minutes  we  notice  that  a  thin  film  of  moisture 
is  accumulating  on  the  inner  surface  of  the  glass  jar.  After  an 
hour  or  more  the  moisture  has  accumulated  so  that  it  appears  in 
the  form  of  small  drops  of  condensed  water.  We  should  set  up 
at  the  same  time  a  bell  jar  in  exactly  the  same  way  but  which 
contains  no  leaves.  In  this  jar  there  is  no  condensed  moisture 
on  the  inner  surface.  We  thus  are  justified  in  concluding  that 


Fig.  47- 

After  a  few  hours  drops  of  water  have  accumulated  on  the  inside  of  the  jar  covering 

the  leaves. 


the  moisture  in  the  former  jar  comes  from  the  leaves.  Since 
there  is  no  visible  water  on  the  surfaces  of  the  leaves,  or  at  the 
cut  ends,  before  it  may  have  condensed  there,  we  infer  that  the 
water  escapes  from  the  leaves  in  the  form  of  water  vapor,  and 
that  this  water  vapor,  when  it  comes  in  contact  with  the  surface 
of  the  cold  glass,  condenses  and  forms  the  moisture  film,  and 
later  the  drops  of  water.  The  leaves  of  these  cut  shoots  there- 
fore lose  water  in  the  form  of  water  vapor,  and  thus  a  loss  of 
turgidity  results. 

70.  Loss  of  water  from  growing  plants. — Suppose  we  now 
take  a  small  and  actively  growing  plant  in  a  pot,  and  cover  the 
pot  and  the  soil  with  a  sheet  of  rubber  cloth  or  flexible  oilcloth 


7"RA  NSPIRA  TION.  3  / 

which  fits  tightly  around  the  stem  of  the  plant  so  that  the  mois- 
ture from  the  soil  or  from  the  surface  of  the  pot  cannot  escape. 
Then  place  a  bell  jar  over  the  plant,  and  set  in  a  brightly  lighted 
place,  at  a  temperature  suitable  for  growth.  In  the  course  of  a 
few  minutes  on  a  dry  day  a  moisture  film  forms  on  the  inner 
surface  of  the  glass,  just  as  it  did  in  the  case  of  the  glass  jar  con- 
taining the  cut  shoots  and  leaves.  Later  the  moisture  has  con- 
densed so  that  it  is  in  the  form  of  drops.  If  we  have  the  same 
leaf  surface  here  as  we  had  with  the  cut  shoots,  we  shall  prob- 
ably find  that  a  larger  amount  of  water  accumulates  on  the 
surface  of  the  jar  from  the  plant  that  is  still  attached  to  its 
roots. 

71.  Water  escapes  from  the  surfaces  of  living  leaves  in  the 
form  of  water  vapor. — This  living  plant  then  has  lost  water,  which 
also  escapes  in  the  form  of  water  vapor.     Since  here  there  are  no 
cut  places  on  the  shoots  or  leaves,  we  infer  that  the  loss  of  water 
vapor  takes  place  from  the  surfaces  of  the  leaves  and  from  the 
shoots.     It  is  also  to  be  noted  that,  while  this  plant  is  losing 
water  from  the  surfaces  of  the  leaves,  it  does  not  wilt  or  lose  its 
turgidity.     The  roots  by  their  activity  and  pressure  supply  water 
to  take  the  place  of  that  which  is  given  off  in  the  form  of  water 
vapor.     This  loss  of  water  in  the  form  of  water  vapor  by  plants 
is  transpiration. 

72.  A  test  for  the  escape  of  water  vapor  from  plants. — Make 
a  solution  of  cobalt  chloride  in  water.     Saturate  several  pieces  of 
filter  paper  with  it.     Allow  them  to  dry.     The  water  solution  of 
cobalt  chloride  is  red.     The  paper  is  also  red  when  it  is  moist, 
but  when  it   is   thoroughly  dry  it   is   blue.     It   is  very  sensitive 
to   moisture   and   the   moisture  of  the  air  is  often   sufficient  to 
redden  it.     Before  using  dry  the  paper  in  an  oven  or  over  a 
flame. 

73.  Take  two  bell  jars,  as  shown  in  fig.  49.     Under  one  place 
a  potted  plant,  the  pot  and  earth  being  covered  by  oiled  paper. 
Or  cover  the  plant  with  a  fruit  jar.     To  a  stake  in  the  pot  pin  a 
piece  of  the  dried  cobalt  paper,  and  at  the  same  time  pin  to  a 


38  PHYSIO  LOG  y. 

stake,  in  another  jar  covering  no  plant,  another  piece  of  cobalt 
paper.  They  should  both  be  put  under  the  jars  at  the  same 
time.  In  a  few  moments  the  paper  in  the  jar  with  the  plant  will 
begin  to  redden.  In  a  short  while,  ten  or  fifteen  minutes,  prob- 
ably, it  will  be  entirely  red,  while  the  paper  under  the  other  jar 
will  remain  blue,  or  be  only  slightly  reddened.  The  water  vapor 
passing  off  from  the  living  plant  comes  in  contact  with  the  sensi- 


ig-  48.  Fig.  49. 

Fig.  48.— Water  vapor  is  given  off  by  the  leaves  when  attached  to  the  living  plant- 
It  condenses  into  drops  of  water  on  the  cool  surface  of  the  glass  covering  the  plant 

tig.  49.— A  good  way  to  show  that  the  water  passes  off  from  the  leaves  in  the  form 
of  water  vapor. 


tive  cobalt  chloride  in  the  paper  and  reddens  it  before  there  is 
sufficient  vapor  present  to  condense  as  a  film  of  moisture  on  the 
surface  of  the  jar. 

74.  Experiment  to  compare  loss  of  water  in  a  dry  and  a 
humid  atmosphere. — We  should  now  compare  the  escape  of 
water  from  the  leaves  of  a  plant  covered  by  a  bell  jar,  as  in  the 
last  experiment,  with  that  which  takes  place  when  the  plant  is 


TRANSPIRA  TION.  39 

exposed  in  a  normal  way  in  the  air  of  the  room  or  in  the  open. 
To  do  this  we  should  select  two  plants  of  the  same  kind  growing 
in  pots,  and  of  approximately  the  same  leaf  surface.  The  potted 
plants  are  placed  one  each  on  the  arms  of  a  scale.  One  of  the 
plants  is  covered  in  this  position  with  a  bell  jar.  With  weights 
placed  on  the  pan  of  the  other  arm  the  two  sides  are  balanced. 
In  the  course  of  an  hour,  if  the  air  of  the  room  is  dry,  moisture 
has  probably  accumulated  on  the  inner  surface  of  the  glass  jar 
which  is  used  to  cover  one  of  the  plants.  This  indicates  that 
there  has  here  been  a  loss  of  water.  But  there  is  no  escape  of 
water  vapor  into  the  surrounding  air  so  that  the  weight  on  this 
arm  is  practically  the  same  as  at  the  beginning  of  the  experiment. 
We  see,  however,  that  the  other  arm  of  the  balance  has  risen. 
We  infer  that  this  is  the  result  of  the  loss  of  water  vapor  from  the 
plant  on  that  arm.  Now  let  us  remove  the  bell  jar  from  the  other 
plant,  and  with  a  cloth  wipe  off  all  the  moisture  from  the  inner 
surface,  and  replace  the  jar  over  the  plant.  We  note  that  the 
end  of  the  scale  which  holds  this  plant  is  still  lower  than  the 
other  end. 

75.  The  loss  of  water  is  greater  in  a  dry  than  in  a  humid 
atmosphere. — This  teaches  us  that  while  water  vapor  escaped 
from  the  plant  under  the  bell  jar,  the  air  in  this  receiver  soon 
became  saturated  with  the  moisture,  and  thus  the  farther  escape 
of  moisture  from  the  leaves  was  checked.     It  also  teaches  us  an- 
other very  important  fact,  viz. ,  that  plants  lose  water  more  rapidly 
through  their  leaves  in  a  dry  air  than  in  a  humid  or  moist  atmos- 
phere.    We  can  now  understand  why  it  is  that  during  the  very 
hot  and  dry  part  of  certain  days  plants  often  wilt,  while  at  night- 
fall, when  the  atmosphere  is  more  humid,  they  revive.     They  lose 
more  water  through  their  leaves  during  the  dry  part  of  the  day, 
other  things  being  equal,  than  at  other  times. 

76.  How  transpiration  takes  place. — Since   the  water  of 
transpiration  passes  off  in  the  form  of  water  vapor  we  are  led  to 
inquire  if  this  process  is  simply  evaporation  of  water  through  the 
surface  of  the  leaves,  or  whether  it  is  controlled  to  any  appreci- 
able extent  by  any  condition  of  the  living  plant.     An  experiment 


4O  PHYSIOLOGY. 

which  is  instructive  in  this  respect  we  shall  find  in  a  comparison 
between  the  transpiration  of  water  from  the  leaves  of  a  cut  shoot, 
allowed  to  lie  unprotected  in  a  dry  room,  and  a  similar  cut  shoot 
the  leaves  of  which  have  been  killed. 

77.  Almost  any  plant  will  answer  for  the  experiment.     For  this  purpose  I 
have  used  the  following  method.     Small  branches  of  the  locust  (Robinia 
pseudacacia),  of  sweet   clover    (Melilotus    alba),  and   of  a   heliopsis    were 
selected.     One  set  of  the  shoots  was  immersed  for  a  moment  in  hot  water  near 
the  boiling  point  to  kill  them.     The  other  set  was  immersed  for  the  same 
length  of  time  in  cold  water,  so  that  the  surfaces  of  the  leaves  might  be  well 
wetted,  and  thus  the  two  sets"  of  leaves  at  the  beginning  of  the  experiment 
would  be  similar,  so  far  as  the  amount  of  water  on  their  surfaces  is  con- 
cerned.    All  the  shoots  were  then  spread  out  on  a  table  in  a  dry  room,  the 
leaves  of  the  killed  shoots  being  separated  where  they  are  inclined  to  cling 
together.     In  a  short  while  all  the  water  has  evaporated  from  the  surface  of 
the  living  leaves,  while  the  leaves  of  the  dead  shoots  are  still  wet  on  the  sur- 
face.    In  six  hours  the  leaves  of  the  dead  shoots  from  which  the  surface 
water  had  now  evaporated  were  beginning  to  dry  up,  while  the  leaves  of  the 
living  plants  were  only  becoming  flaccid^    In  twenty -four  -hours  the  leaves 
of  the  dead  shoots  were  crisp  and  brittle,  while  thoJfe  of  the  living  shoots  were 
only  wilted.     In  twenty-four  hours  more  the  leaves  of  the  sweet  clover  and 
of  the  heliopsis  were  still  soft  and  flexible,  showing  that  they  still  contained 
more  water  than  the  killed  shoots  which  had  been  crisp  for  more  than  a 
day. 

78.  It  must  be  then  that  during  what  is  termed  transpiration  the  living 
plant  is  capable  of  holding  back  the  water  to  some  extent,  which  in  a  dead 
plant  would  escape  more  rapidly  by  evaporation.     It  is  also  known  that  a 
body  of  water  with  a  surface  equal  to  that  of  .a  given  leaf  surface  of  a  plant 
loses  more  water  by  evaporation  during  the  same  length  of  time  than  the 
plant  loses  by  transpiration. 

79.  Structure  of  a  leaf. — We  are  now  led  to  inquire  why  it  is 
that  a  living  leaf  loses  water  less  rapidly  than  dead  ones,  and 
why  less  water  escapes  from  a  given  leaf  surface  than  from  an 
equal  surface  of  water.  To  understand  this  it  will  be  necessary 
to  examine  the  minute  structure  of  a  leaf.  For  this  purpose  we 
may  select  the  leaf  of  an  ivy,  though  many  other  leaves  will 
answer  equally  well.  From  a  portion  of  the  leaf  we  should  make 
very  thin  cross  sections  with  a  razor  or  other  sharp  instrument. 
These  sections  should  be  perpendicular  to  the  surface  of  the  leaf 


TRANSPIRA  TION. 


and  should  be  then  mounted  in  water  for  microscopic  examina- 
tion.* 

80.  Epidermis  of  the  leaf. — In  this  section  we  see  that  the 
green   part  of  the  leaf  is  bordered  on  what  are  its  upper  and 
lower  surfaces  by  a  row  of  cells  which 

possess  no  green  color.  The  walls  of 
the  cells  of  each  row  have  nearly  par- 
allel sides,  and  the  cross  walls  are  per- 
pendicular. These  cells  form  a  single 
layer  over  both  surfaces  of  the  leaf  and 
are  termed  the  epidermis.  Their  walls 
are  quite  stout  and  the  outer  walls  are 
cuticularized. 

81.  Soft  tissue  of  the  leaf.— The 
cells  which  contain  the  green  chloro- 
phyll bodies  are  arranged  in  two  dif-  , 

Section  through  ivy  leaf  showing 
ferent  Ways.       Those  On  the  upper  side  communication  between  stomate and 

*  the  large  intercellular  spaces.of  the 

of  the   leaf  are  usually  long  and  pris-  leaf;  stoma  closed. 
matic  in  form  and  lie  closely  parallel  to  each  other.      Because  of 
this  arrangement  of  these  cells  they  are  termed  the  palisade  cells, 
and  form  what  is  called  the  palisade  layer.     The  other  green 

cells,  lying  below, 
vary  greatly  in  size  in 
different  plants  and  to 
some  extent  also  in  the 
same  plant.  Here  we 
notice  that  they  are 
elongated,  or  oval,  or 
somewhat  irregular  in 
form.  The  most  striking  peculiarity,  however,  in  their  arrange- 
ment is  th.'.*t  they  are  not  usually  packed  closely  together,  but  each 
cell  touches  the  other  adjacent  cells  only  at  certain  points.  This 
arrangement  of  these  cells  forms  quite  large  spaces  between  them, 
the  intercellular  spaces.  If  we  should  examine  such  a  section  of 
a  leaf  before  it  is  mounted  in  water  we  would  see  that  the  inter- 


Fig.  51. 

Stoma  open. 
Figs.  34,  35. — Section  through  stomata  of  ivy  leaf. 


Fig.  52. 
Stoma  closed. 


*  Demonstrations  may  be  made  with  prepared  sections  of  leaves. 


42  PHYSIO  LOG  Y. 

cellular  spaces  are  not  filled  with  water  or  cell-sap,  but  are  filled 
with  air  or  some  gas.  Within  the  cells,  on  the  other  hand,  we 
find  the  cell-sap  and  the  protoplasm. 

82.  Stomata. — If  we  examine  carefully  the  row  of  epidermal 
cells  on  the  under  surface  of  the  leaf,  we  find  here  and  there 
a  peculiar  arrangement  of  cells  shown  at  figs.  51,  52.  This 

opening 
through  the 
epidermal 
layer  is  a 
sioma.  The 
cells  which 
i  m  mediately 
surround  the 
openings  are 

the      guard 
Fis-  S3.  „         ™, 

Portion  of  epidermis   of  ivy,  showing  irregular  epidermal  cells,  stoma  C6US.  1  n  C 


form    of  the 

guard  cells  can  be  better  seen  if  we  tear  a  leaf  in  such  a  way  as 
to  strip  off  a  short  piece  of  the  lower  epidermis,  and  mount  this 
in  water.  The  guard  cells  are  nearly  crescent  shaped,  and  the 
stoma  is  elliptical  in  outline.  The  epidermal  cells  are  very 
irregular  in  outline  in  this  view.  We,  should  also  note  that  while 
the  epidermal  cells  contain  no  chlorophyll,  the  guard  cells  do. 

820.  In  the  ivy  leaf  the  guard  cells  are  quite  plain,  but  in  most 
plants  the  form  as  seen  in  cross-section  is  irregular  in  outline,  as 
shown  in  fig.  530,  which  is  from  a  section  of  a  wintergreen  leaf. 
This  leaf  is  interesting  because  it  shows  the  characteristic  struc- 
ture of  leaves  of  many  plants  growing  in  soil  where  absorption  of 
water  by  the  roots  is  difficult  owing  to  the  cold  water,  acids,  or 
salts  in  the  water  or  soil,  or  in  dry  soil  (see  Chapters  47,  54,  55). 
The  cuticle  over  the  upper  epidermis  is  quite  thick.  This 
lessens  the  loss  of  water  by  the  leaf.  The  compact  palisades  of 
cells  are  in  two  to  three  cell  layers,  also  reducing  the  loss  of  water. 

83.  The  living  protoplasm  retards  the  evaporation  of  water  from  the 
leaf. — If  we  now  take  into  consideration  a  few  facts  which  we  have  learned 


TRANSPIRA  TION. 


43 


in  a  previous  chapter,  with  reference  to  the  physical  properties  of  the  living 
cell,  we  shall  be  able  to  give  a  partial  explanation  of  the  comparative  slow- 
ness with  which  the  water  escapes  from  the  leaves.  The  inner  surfaces  of 
the  cell  walls  are  lined  with  the  membrane  of  protoplasm,  and  within  this 
is  the  cell-sap.  These  cells  have  become  turgid  by  the  absorption  of  the 


Fig.  530. 

Cross-section  of  leaf  of  wintergreen.     Cu,  cuticle;  Epid.,  epidermis;  v.d.,  vascular 
duct;   Int.  c.  sp.,  intercellular  space;    L.  ep.,  lower  epidermis;   St.,  stoma. 


water  which  has  passed  up  to  them  from  the  roots.  While  the  protoplas- 
mic membrane  of  the  cells  does  not  readily  permit  the  water  to  filter  through, 
yet  it  is  saturated  with  water,  and  the  elastic  cell  wall  with  which  it  is  in 
contact  is  also  saturated.  From  the  cell  wall  the  water  evaporates  into  the 
intercellular  spaces.  But  the  water  is  given  up  slowly  through  the  proto- 
plasmic membrane,  so  that  the  water  vapor  cannot  be  given  off  as  rapidly 
from  the  cell  walls  as  it  could  if  the  protoplasm  were  dead.  The  living 
protoplasmic  membrane  then  which  is  only  slowly  permeable  to  the  water  of 
the  cell-sap  is  here  a  very  important  factor  in  checking  the  too  rapid  loss  of 
water  from  the  leaves. 


44  PHYSIO  LOG  Y. 

By  an  examination  of  our  leaf  section  we  see  that  the  intercellulai  spaces 
are  all  connected,  and  that  the  stomata,  where  they  occur,  open  also  into 
intercellular  spaces.  There  is  here  an  opportunity  for  the  water  vapoi 
in  the  intercellular  spaces  to  escape  when  the  stomata  are  open, 

84.  Action  of  the  stomata. — The  guard  cells  serve  an  important  func- 
tion in  regulating  transpiration.     During  normal  transpiration  the  guard 
cells  are  turgid  and  their  peculiar  form  then  causes  them  to  arch  away 
from  each  other,  allowing  the  escape  of  water  vapor.     When  the  air  becomes 
too  dry  transpiration  is  in  excess  of  absorption  by  the  roots.     The  guard 
cells  lose  some  of  their  v/ater,  and  collapse  so  that  their  inner  faces  meet 
in  a  straight  line  and  close  the  stoma.     Thus  the  rapid  transpiration  is 
checked.     Some  evaporation  of  water  vapor,  however,  takes  place  through 
the  epidermal  cells,  and  if  the  air  remains  too  dry,  the  leaves  eventually 
become  flaccid  and  droop.     During  the  day  the  effect  of  sunlight  is  to 
increase  certain  sugars  or  salts  in  the  guard  cells  so  that  they  readily  be- 
come turgid  and  open  the  stomates,  but  at  night  the  cell-sap  is  less  con- 
centrated  and   the   stomates   are  usually   closed.     Light   therefore   favors 
transpiration,  while  in  darkness  transpiration  is  checked. 

85.  Compare  transpiration  from  the  two  surfaces  of  the  leaf. — This  can 
be  done  by  using  the  cobalt  chloride  paper.     This  paper  can  be  kept  from 
year  to  year  and  used  repeatedly.     It  is  thus  a  very  simple  matter  to  make 
these  experiments.     Provide   two  pieces  of  glass   (discarded   glass   nega- 
tives, cleaned,  are  excellent),  two  pieces  of  cobalt  chloride  paper,  and  some 
geranium  leaves  entirely  free  from  surface  water.     Dry  the  paper  until  it  is 
blue.     Place  one  piece  of  the  paper  on  a  glass  plate;    place  the  geranium 
leaf  with  the  under  side  on  the  paper.     On  the  upper  side  of  the  leaf  now 
place  the  other  cobalt  paper,  and  next  the  second  piece  of  glass.     On  the 
pile  place  a  light  weight  to  keep  the  parts  well  in  contact.     In  fifteen  or 
twenty  minutes  open  and  examine.     The  paper  next  the  under  side  of  the 
geranium  leaf  is  red  where  it  lies  under  the  leaf.     The  paper  on  the  upper 
side  is  only  slightly  reddened.     The  greater  loss  of  water,  then,  is  through 
the  under  side  of  the  geranium  leaf.     This  is  true  of  a  great  many  leaves, 
but  it  is  not  true  of  all. 

86.  Negative  pressure. — This  is  not  only  indicated  by  the  drooping  of 
the  leaves,  but  may  be  determined  in  another  way.     If  the  shoot  of  such  a 
plant  be  cut  underneath  mercury,  or  underneath  a  strong  solution  of  eosin, 
it  will  be  found  that  some  of  the  mercury  or  eosin,  as  the  case  may  be,  will 
be  forcibly  drawn  up  into  the  stem  toward  the  roots.     This  is  seen  on 
quickly  splitting  the  cut  end  of  the  stem.     When  plants  in  the  open  cannot 
be  obtained  in  this  condition,  one  may  take  a  plant  like  a  balsam  plant 
from  the  greenhouse,  or  some  other  potted  plant,  knock  it  out  of  the  pot, 
free  the  roots  from  the  soil  and  allow  to  partly  wilt.     The  stem  may  then 
be  held  under  the  eosin  solution  and  cut. 


TRANSPIRA  TION; 


45 


Fig.  54- 
Experiment  to 


87.  Lifting  power  of  transpiration.  — Not  only  does  transpiration  go  on 
quite  independently  of  root  pressure,   as  we  have  discovered  from  other 
experiments,  but  transpiration  is  capable  of  exerting  a 

lifting  power  on  the  water  in  the  plant.  This  may 
be  demonstrated  in  the  following  way:  Place  the  cut 
end  of  a  leafy  shoot  in  one  end  of  a  U  tube  and  fit  it 
water-tight.  Partly  fill  this  arm  of  the  U  tube  with 
water,  and  add  mercury  to  the  other  arm  until  it 
stands  at  a  level  in  the  two  arms  as  in  fig.  54.  In  a 
short  time  we  note  that  the  mercury  is  rising  in  the 
tube. 

88.  Root  pressure  may  exceed  transpiration. — If  we 
cover  small  actively  growing  plants,  such  as  the  pea, 
corn,  wheat,  bean,  etc.,  with  a  bell  jar,  and  place  them 
in  the  sunlight  where    the  temperature  is  suitable  for 
growth,  in  a  few  hours,  if  conditions  are  favorable, 
we  shall  see  that  there  are  drops  of  water  standing  out 
on  the  margins  of  the  leaves.     These  drops  of  water 

have    exuded    through    the    ordinary    stomata,    or    in    show  lifting  power  of 
other  cases  what  are  called  water  stomata,   through 

the  influence  of  root  pressure.  The  plant  being  covered  by  the  glass  jar, 
the  air  soon  becomes  saturated  with  moisture  and  transpiration  is  checked. 
Root  pressure  still  goes  on,  however,  and  the  result  is  shown  in  the  exuding 
drops.  Root  pressure  is  here  in  excess  of  transpiration. 
This  phenomenon  is  often  to  be  observed  during  the  sum- 
mer season  in  the  case  of  low-growing  plants.  During  the 
bright  warm  day  transpiration 

"  '  equals,  or  may  be  in  excess  of, 

Fig  ss<  root  pressure,  and  the  leaves 

Estimation  of  the  amount  of  are  consequently  flaccid.     As 

fined^wUh^water     and1  as   the  nigntfaU     comes     on     the    air 

water   transpires  from  the  leaf  becomes  more  moist,  and  the 
surface  its  movement  in  the  tubs 

from  a  to  b  can  be   measured,  conditions   of    light    are    such 

also  that  transpiration  is  les- 
sened.  Root  pressure,  however,  is  still  active  because  the  soil  is  still  warm. 
In  these  cases  drops  of  water  may  be  seen  exuding  from  the  margins  of  the 
leaves  due  to  the  excess  of  root  pressure  over  transpiration.  Were  it  not 
for  this  provision  for  the  escape  of  the  excess  of  water  raised  by  root  pres- 
sure, serious  injury  by  lesions,  as  a  result  of  the  great  pressure,  might 
result.  The  plant  is  thus  to  some  extent  a  self-regulatory  piece  of 
apparatus  so  far  as  root  pressure  and  transpiration  are  concerned. 

89.  Injuries  caused  by  excessive  root  pressure.— Some  varieties  of  toma- 
toes when  grown  in  poorly  lighted  and  poorly  ventilated  greenhouses  suffer 


46 


PHYSIOLOGY. 


serious  injury  through  lesions  of  the  tissues.  This  is  brought  about  by  the 
cells  at  certain  parts  becoming  charged  so  full  with  water  through  the 
activity  of  root  pressure  and  lessened  transpiration,  assisted  also  probably 
by  an  accumulation  of  certain  acids  in  the  cell-sap  which  cannot  be  got 
rid  of  by  transpiration.  Under  these  conditions  some  of  the  cells  here 
swell  out,  forming  extensive  cushions,  and  the  cell  walls  become  so  weak- 
ened that  they  burst.  It  is  possible  to  imitate  the  excess  of  root  pressure 
in  the  case  of  some  plants  by  connecting  the  stems  with  a  system  of 

water  pressure,  when  very  quickly 
the  drops  of  water  will  begin  to 
exude  from  the  margins  of  the 
leaves. 

90.  It  should  be  stated   that  in 
reality  there  is  no  difference  between 
transpiration  and  evaporation,  if  we 
bear  in  mind  that  evaporation  takes 
place  more  slowly  from  living  plants 
than  from  dead  ones,  or  from  an 
equal  surface  of  water. 

91.  The  escape  of  water  vapor  is 
not  the  only  function  of  the  stomata. 
The  exchange  of  gases  takes  place 
through  them  as  we  shall  later  see. 
A  large  number  of  experiments  show 
that  normally  the  stomata  are  open 
when  the   leaves  are   turgid.      But 
when  plants  lose  excessive  quantities 
of  water  on  dry  and  hot  days,  so 
that  the  leaves  become  flaccid,  the 
guard  cells  automatically  close  the 

Fig.  56.  stomata  to  check  the  escape  of  water 

The  roots  are  lifting  more  water  into    VJ,nr._       Qr>rnf>  ™atm- ^cr^r^c  f^™nrrV. 

the  plant  than  can  be  giyen  off  in  the  form    vaP°r-      ^ome  water  escapes  through 

of  water  vapor,  so  it  is  pressed  out  in    the     epidermis     of     many    plants, 

drops.     From  "  First  Studies  Plant  Life.  ' 

though  the  cuticulanzed  mem- 
brane of  the  epidermis  largely  prevents  evaporation.  In  arid  regions 
plants  are  usually  provided  with  an  epidermis  of  several  layers  of  cells  to 
more  securely  prevent  evaporation  there.  In  such  cases  the  guard  cells 
are  often  protected  by  being  sunk  deeply  in  the  epidermal  layer. 

92.  Demonstration  of  stomates  and  intercellular  air  spaces. — A  good 
demonstration  of  the  presence  of  stomates  in  leaves,  as  well  as  the  presence 
and  intercommunication  of  the  intercellular  spaces,  can  be  made  by  blow- 
ing into  the  cut  end  of  the  petiole  of  the  leaf  of  a  calla  lily,  the  lamina  being 


TRANSPIRA  TION.  47 

immersed  in  water.  The  air  is  forced  out  through  the  stomata  and  rises  as 
bubbles  to  the  surface  of  the  water.  A.t  the  close  of  the  experiment  soir.e 
of  the  air  bubbles  will  still  be  in  contact  with  the  leaf  surface  at  the  opening 
of  the  stomata.  The  pressure  of  the  water  gradually  forces  this  back  into 
the  leaf.  Other  plants  will  answer  for  the  experiment,  but  some  are  more 
suitable  than  others. 

92a.  Number  of  stomata. — The  larger  number  of  stomata  are  on  the 
under  side  of  the  leaf.  (In  leaves  which  float  on  the  surface  of  the  water 
all  of  the  stomata  are  on  the  upper  side  of  the  leaf,  as  in  the  water  lily.)  It 
has  been  estimated  by  investigation  that  in  general  there  are  40-300  stomata 
to  the  square  millimeter  of  surface.  In  some  plants  this  number  is  exceeded, 
as  in  the  olive,  where  there  are  625.  In  an  entire  leaf  of  Brassica  rapa 
there  are  about  11,000,000  stomata,  and  in  an  entire  leaf  of  the  sunflower 
there  are  about  13,000,000  stomata. 

92b.  Amount  of  water  transpired  by  plants. — The  amount  of  water 
transpired  by  plants  is  very  great.  According  to  careful  estimates  a  sun- 
flower 6  feet  high  transpires  on  the  average  about  one  quart  per  day;  an 
acre  of  cabbages  2,000,000  quarts  in  four  months;  an  oak  tree  with  700,000 
leaves  transpires  about  180  gallons  of  water  per  day.  According  to  von  Hoh- 
nel,  a  beech  tree  no  years  old  transpired  about  2250  gallons  of  water  in 
one  summer.  A  hectare  of  such  trees  (about  400  on  2^  acres)  would  at  the 
same  rate  transpire  about  900,000  gallons,  or  about  30,000  barrels  in  one 
summer. 


CHAPTER  V. 

PATH    OF   MOVEMENT   OF  WATER   IN    PLANTS. 

93.  In  our  study  of  root  pressure  and  transpiration  we  have 
seen  that  large  quantities  of  water  or  solutions  move  upward 
through    the    stems  of  plants.       We    are    now  led    to    inquire 
through  what  part  of  the  stems  the  liquid  passes  in  this  upward 
movement,  or  in  other  words,  what  is  the  path  of  the  "sap"  as 
it  rises  in  the  stem.     This  we  can  readily  see  by  the  following 
trial. 

94.  Place  the  cut  ends  of  leafy  shoots  in  a  solution  of  some 
of  the  red  dyes. — We  may  cut  off  leafy  shoots  of  various  plants 
and  insert  the  cut  ends  in  a  vessel  of  water  to  which  have  been 
added  a  few  crystals  of  the  dye  known  as  fuchsin  to  make  a  deep 
red  color  (other  red  dyes  may  be  used,  but  this  one  is  especially 
good).     If  the  study  is  made  during  the  summer,  the  "touch- 
me-not"  (impatiens)  will  be  found  a  very  useful  plant,  or  the 
garden -balsam,  which  may  also  be  had  in  the  winter  from  con- 
servatories.    Almost  any  plant  will  do,  however,  but  we  should 
also  select  one  like  the  corn  plant  (zea  mays)  if  in  the  summer, 
or  the  petioles  of  a  plant  like  caladium,  which  can  be  obtained 
from  the  conservatory.      If  seedlings  of  the  castor-oil  bean  are  at 
hand  we  may  cut  off  some  shoots  which  are  8-10  inches  high, 
and  place  them  in  the  solution  also. 

95.  These  solutions  color  the  tracts  in  the  stem  and  leaves 
through  which  they  flow. — After  a  few  hours  in  the  case  of  the 
impatiens,  or  the  more  tender  plants,  we  can  see  through  the 
stem  that  certain  tracts  are  colored  red  by   the  solution,   and 
after  12  to  24  hours  there  may  be  seen  a  red  coloration  of  the 

48 


PATH  OF  MOVEMENT:  49 

leaves  of  some  of  the  plants  used.  After  the  shoots  have  been 
standing  in  the  solution  for  a  few  hours,  if  we  cut  them  at 
various  places  we  will  note  that  there  are  several  points  in  the 
section  where  the  tissues  are  colored  red.  In  the  impatiens 
perhaps  from  four  to  five,  in  the  sunflower  a  larger  number.  In 
these  plants  the  colored  areas  on  a  cross  section  of  the  stem  are 
situated  in  a  concentric  ring  which  separates  more  or  less  com- 
pletely an  outer  ring  of  the  stem  from  the  central  portion.  If 
we  now  split  portions  of  the  stem  lengthwise  we  see  that  these 
colored  areas  continue  throughout  the  length  of  the  stem,  in  some 
cases  even  up  to  the  leaves  and  into  them. 

96.  If  we  cut  across  the  stem  of  a  corn  plant  which  has  been 
in  the  solution,  we  see  that  instead  of  the  colored  areas  being  in 
a  concentric  ring  they  are  irregularly  scattered,  and  on  splitting 


Fig.  57. 
Broken  corn  stalk,  showing  nbro-vascular  bundles. 

the  stem  we  see  here  also  that  these  colored  areas  extend  for  long 
distances  through  the  stem.  If  we  take  a  corn  stem  which  is 
mature,  or  an  old  and  dead  one,  cut  around  through  the  outer 
hard  tissues,  and  then  break  the  stem  at  this  point,  from  the 
softer  tissue  long  strings  of  tissue  will  pull  out  as  shown  in  fig. 
57.  These  strings  of  denser  tissue  correspond  to  the  areas 
which  are  colored  by  the  dye.  They  are  in  the  form  of  minute 
bundles,  and  are  called  vascular  bundles. 


5O  PHYSIO  LOG  V. 

97.  We  thus  see  that  instead  of  the  liquids  passing  through 
the  entire  stem  they  are  confined  to  definite  courses.  Now  that 
we  have  discovered  the  path  of  the  upward  movement  of  water 
in  the  stem,  we  are  curious  to  see  what  the  structure  of  these 
definite  portions  of  the  stem  is. 

98.  Structure  of  the  fibre-vascular  bundles. — We  should  now  make  quite 
thin  cross  sections,  either  free  hand  and  mount  in  water  for  microscopic 
examination,  or  they  may  be  made  with  a  microtome  and  mounted  in  Canada 
balsam,  and  in  this  condition  will  answer  for  future  study.  To  illustrate  the 
structure  of  the  bundle  in  one  type  we  may  take  the  stem  of  the  castor-oil 
bean.  On  examining  these  cross  sections  we  see  that  there  are  groups  of 
cells  which  are  denser  than  the  ground  tissue.  These  groups  correspond  to 
the  colored  areas  in  the  former  experiments,  and  are  the  vascular  bundles 


> 

Fig.  58. 

Xylem  portion  of  bundle.  Cambium  portion  of  bundle.          Bast  portion  of  bundle. 

Section  of  vascular  bundle  of  sunflower  stem. 

cut  across.  These  groups  are  somewhat  oval  in  outline,  with  the  pointed 
end  directed  toward  the  center  of  the  stem.  If  we  look  at  the  section 
as  a  whole  we  see  that  there  is  a  narrow  continuous  ring  *  of  small  cells 

*  This  ring  and  the  bundles  separate  the  stem  into  two  regions,  an  outer 
one  composed  of  large  cells  with  thin  w^alls;  known  as  the  cortical  cells,  or 
collectively  the  cortex.  The  inner  portion,  corresponding  to  what  is  called 
the  pith,  is  made  up  of  the  same  kind  of  cells  and  is  called  the  medulla,  or 
pith.  '  When  the  cells  of  the  cortex,  as  well  as  of  the  pith,  remain  thin  walled 
the  tissue  is  called  parenchyma.  Parenchyma  belongs  to  the  group  of 
tissues  called  fundamental. 


PATH  OF  MOVEMENT.  5 1 

situated  at  the  same  distance  from  the  center  of  the  stem  as  the  middle  part 
of  the  bundles,  and  that  it  divides  the  bundles  into  two  groups  of  cells. 

99.  Woody  portion  of  the  bundle. — In  that  portion  of  the  bundle  on  the 
inside  of  the  ring,  i.e.,  toward  the  "pith,"  we  note  large,  circular,  or  angu- 
lar cavities.     The  walls  of  these  cells  are  quite  thick  and  woody.     They  are 
therefore  called  wood  cells,  and  because  they  are  continuous  with  cells  above 
and  below  them  in  the  stem  in  such  a  way  that  long  tubes  are  formed,  they 
are  called  woody  vessels.     Mixed  in  with  these  are  smaller  cells,  some  of 
which  also  have  thick  walls  and  are  wood  cells.     Some  of  these  cells  may 
have  thin  walls.     This  f  is  the  case  with  all  when  they  are  young,  and  they 
are  then  classed  with  the  fundamental  tissue  or  soft  tissue  (parenchyma). 
This  part  of  the  bundle,  since  it  contains  woody  vessels  and  fibres,  is  the 
wood  portion  of  the  bundle^  or  technically  the  xylem. 

100.  Bast  portion  of  the  bundle. — If  our  section  is  through  a  part  of  the 
stem  which  is  not  too  young,  the  tissues  of  the  outer  part  of  the  bundle  will 
show  either  one  or  several  groups  of  cells  which  have  white  and  shiny  walls, 
that  are  thickened  as  much  or  more  than  those  of  the  wood  vessels.     These 
cells  are  bast  cells,  and  for  this  reason  this  part  of  the  bundle  is  the  bast  por- 
tion, or  the  phloem.     Intermingled  with  these,  cells  may  often  be  found  which 
have  thin  walls,  unless  the  bundle  is  very  old.  v   Nearer  the  center  of  the 
bundle  and  still  within  the  bast  portion  are  cells  with  thin  walls,  angular  and 
irregularly  arranged.     This  is  the  softer  portion  of  the  bast,  and  some  of 
these  cells  are  what  are  called  sieve  tubes,  which  can  be  better  seen  and 
studied  in  a  longitudinal  section  of  the  stem. 

101.  Cambium  region  of  the  bundle. — Extending  across  the  center  of  the 
bundle  are  several  rows  of  small  cells,  the  smallest  of  the  bundle,  and  we  can 
see  that  they  are  more  regularly  arranged,  usually  in  quite  regular  rows, 
like  bricks  piled  upon  one  another.     These  cells  have  thinner  walls  than  any 
others  of  the  bundle,   and  they  usually  take  a  deeper  stain  when  treated 
with  a  solution  of  some  of  the  dyes.     This  is  because  they  are  younger,  and 
are   therefore    richer  in  protoplasmic  contents.     This  zone  of  young  cells 
across  the  bundle  is  the  cambium.    Its  cells  grow  and  divide,  and  thus  increase 
the  size  of  the  bundle.     By  this  increase  in  the  number  of  the  cells  of  the 
cambium  layer,  the  outermost  cells  on  either  side  are  continually  passing 
over  into  the  phloem,  on  the  one  hand,  and  into  the  wood  portion  of  the 
bundle,  on  the  other  hand. 

102.  Longitudinal  section  of  the  bundle. — If  we  make  thin  longisections  of 
the  vascular  bundle  of  the  castor-oil  seedling  (or  other  dicotyledon)  so  that  we 
have  thin  ones  running  through  a  bundle  radially,  as  shown  in  fig.  59,  we 
can  see  the  structure  of  these  parts  of  the  bundle  in  side  view.     We  see  here 
that  the  form  of  the  cells  is  very  different  from  what  is  presented  in  a  cross 
section  of  the  same.     The  walls  of  the  various  ducts  have  peculiar  markings 
on  them.     These  markings  are  caused  by  the  walls  being  thicker  in  some 


52' 


PHYSIOLOGY. 


places  than  in  others,  and  this  thickening  takes  place  so  regularly  in  some 
instances  as  to  form  regular  spiral  thickenings.     Others  have  the  thickenings 


* 


Mm 


ff 

s 

/         „  . 

Fig-  59- 

Longitudinal  section  of  vascular  bundle  of  sunflower  stem  ;  spiral,  scalariform  and  pitted 
vessels  at  left ;  next  are  wood  fibers  with  oblique  cross  walls  ;  in  middle  are  cambium  cells 
with  straight  cross  walls,  next  two  sieve  tubes,  then  phloe'm  or  bast  cells. 

in  the  form  of  the  rounds  of  a  ladder,  while  still  others  have  pitted  wails  or  the 
thickenings  are  in  the  form  of  rings. 

103.  Vessels  or  ducts. — One  way  in   which  the  cells  in  side  view  differ 
greatly  from  an  end  view,  in  a  cross  section  in  the  bundle,  is  that  they  are 
much  longer  in  the  direction  of  the  axis  of  the  stem.     The  cells  have  become 
elongated  greatly.     If  we  search  for  the  place  where  two  of  these  large  cells 
with   spiral,  or    ladder-like,  markings   meet   end   to   end,  we   see   that   the 
wall  which  formerly  separated  the  cells  has  nearly  or  quite  disappeared.     In 
other  words  the  two  cells  have  now  an  open  communication  at  the  ends. 
This  is  so  for  long  distances  in  the  stem,  so  that  long  columns  of  these  large 
cells  form  tubes  or  vessels  through  which  the  water  rises  in  the  stems  of 
plants. 

104.  In  the  bast  portion  of  the  bundle  we  detect  the  cells  of  the  bast  fibers 
by  their  thick  walls.     They  are  very  much  elongated  and  the  ends  taper  out  to 
thin  points  so  that  they  overla  p.    In  this  way  they  serve  to  strengthen  tiie  stem- 

105.  Sieve  tubes. — Lying  near  the  bast  cells,  usually  toward  the  cambium, 
are  elongated  cells  standing  end  to  end,  with  delicate  markings  on  their  cross 
walls  which  appear  like  finely  punctured  plates  or  sieves.     The  protoplasm 
in  such  cells  is  usually  quite  distinct,  and  sometimes  contracted  away  from 
the  sideWalls,  but  attached  to  the  cross  walls,  and  this  aids  in  the  detection 
of  the  sieve  tubes  (fig.  59.)     The  granular  appearance  which  these  plates  pre- 
sent is  caused  by  minute  perforations  through  the  wall  so  that  there  is  a  com- 
munication between  the  cells.     The  tubes  thus  formed  are  therefore  called 
sieve  tubes  and  they  extend  for  long  distances  through  the  tube  so  that  there 


PATH  OF  MOVEMENT. 


53 


is  communic?,tion  throughout  the  entire  length  of  the  stem.  (The  function  of 
the  sieve  tubes  is  supposed  to  be  that  for  the  downward  transportation  of  sub- 
stances elaborated  in  the  leaves.) 

106.  If  we  section  in  like  manner  the  stem  of  the  sunflower  we  shall  see  simi- 
lar bundles,  but  the  number  is  greater  than  eight.     In  the  garden  balsam  the 
number  is  from  four  to  six  in  an  ordinar}'  stem  ^-^mm  diameter.      Here  we 
can  see  quite  well  the  origin  of  the  vascular  bundle.     Between  the  larger 
bundles  we  can  see  especially  in  free-hand  sections  of  stems  through  which 
a  colored  solution  has  been  lifted  by  transpiration,  as  in  our  former  experi- 
ments, small  groups  of  the  minute  cells  in  the  cambial  ring  which  are  colored. 
These  groups  of  cells  which  form  strands  running  through  the  stem  are  pro- 
cambium  strands.     The  cells  divide  and  increase  just  like  the  cambium  cells, 
and  the  older  ones  thrown  off  on  either  side  change,  those  toward  the  center 
of  the  stem  to  wood  vessels  and  fibers,   and  those  on  the  outer  side  to  bast 
cells  and  sieve  tubes. 

107.  Fibrovascular  bundles  in  the  Indian  corn. — We  should  now  make 
a  thin  transection  of  a  portion  of  the  center  of  the  stem  of  Indian  corn,  in 
order   to   compare   the   structure   of    the 

bundle  with  that  of  the  plants  which  we 
have  just  examined.  In  fig.  60  is  repre- 
sented a  fibrovascular  bundle  of  the  stem 
of  the  Indian  corn.  The  large  cells  are 
those  of  the  spiral  and  reticulated  and 
annular  vessels.  This  is  the  woody  por- 
tion of  the  bundle  or  xylem.  Opposite 
this  is  the  bast  portion  or  phloem,  marked 
by  the  lighter  colored  tissue  at  i.  The 
larger  of  these  cells  are  the  sieve  tubes, 
and  intermingled  with  them  are  smaller 
cells  with  thin  walls.  Surrounding  the 
entire  bundle  are  small  cells  with  thick 
walls.  These  are  elongated  and  the  taper- 
ing ends  overlap.  They  are  thus  slender 
and  long  and  form  fibers.  In  such  a 

bundle    all    of  the    cambium    has    passed  vessel  -~r,  annular  vessel ;  /,  air  cavity 

formed  by  breaking  apart  of  the  cells  ;  i, 

over  into  permanent  tissue  and  is  said  to  £0ft  bast,  a  form  of  sieve  tissue ;  /,  thin- 
i  i  i  walled  parenchyma.  (Sachs.; 

108.  Rise  of  water  in  the  vessels. — During  the  movement  of  the  water  or 
nutrient  solutions  upward  in  the  stem  the  vessels  of  the  wood  portion  of  the 
bundle  in  certain  plants  are  nearly  or  quite  filled,  if  root  pressure  fs  active 
and  transpiration  is  not  very  rapid.     If,  however,  on  dry  days  transpiration 
is  in  excess  of  root  pressure,  as  often  happens,  the  vessels  are  not  filled  with 
the  water,  but  are  partly  filled  with  certain  gases  because  the  air  or  other 


Fig-  60. 

Transaction  of  fibrovascular  bundle  of 
Indian  corn.  a,  toward  periphery  of 
stem  ;  g,  large  pitted  vessels ;  s,  spiral 


54  PHYSIOLOGY. 

gases  in  the  plant  become  rarefied  as  a  result  of  the  excessive  loss  of  water. 
There  are  then  successive  rows  of  air  or  gas  bubbles  in  the  vessels  separated 
by  films  of  water  which-  also  line  the  walls  of  the  vessels.  The  condition  of 
the  vessel  is  much  like  that  of  a  glass  tube  through  which  one  might  pass  the 
"froth  "  which  is  formed  on  the  surface  of  soapy  water.  This  forms  a  chain 
of  bubbles  in  the  vessels.  This  chain  has  been  called  Jamin's  chain  because 
of  the  discoverer. 

109  Why  water  or  food  solutions  can  be  raised  by  the  plant  to  the  height 
attained  by  some  trees  has  never  been  satisfactorily  explained.  There  are 
several  theories  propounded  which  cannot  be  discussed  here.  It  is  probably 
a  very  complex  process.  Root  pressure  and  transpiration  both  play  a  part, 
or  at  least  can  be  shown,  as  we  have  seen,  to  be  capable  of  lifting  water  to  a 
considerable  height.  In  addition  to  this,  the  walls  of  the  vessels  absorb  water 
by  diffusion,  and  in  the  other  elements  of  the  bundle  capillarity  comes  also 
into  play,  as  well  as  osmosis. 

See  Organization  of  Tissues,  Chapter  38. 

110.  Flow  of  sap  in  the  spring. — The  cause  of  the  bleeding  of  trees  and 
the  flow  of  sap  in  the  spring  is  little  understood.  One  of  the  remarkable 
cases  is  the  flow  of  sap  in  maple  trees.  It  begins  in  early  spring  and  ceases 
as  the  buds  are  opening,  and  seems  to  be  initiated  by  alternation  of  high 
and  low  temperatures  of  day  and  night.  It  has  been  found  that  the  pres- 
sures inside  of  the  tree  at  this  time  are  enormously  increased  during  the 
day,  when  the  temperature  rises  after  a  cold  night.  This  has  led  to  the 
belief  that  the  pressure  is  caused  by  the  expansion  of  the  gases  in  the  vas- 
cular ducts.  The  warming  up  of  the  twigs  and  branches  of  the  tree  would 
take  place  rapidly  during  the  day,  while  the  interior  of  the  trunk  would  be 
only  slightly  affected.  The  pressures  then  would  cause  the  sap  to  flow 
downward  during  the  day,  and  at  night  the  branches  becoming  cool,  sap 
would  flow  back  again  from  the  roots  and  trunk 

Recent  experiments  by  Jones  et  al.  show  that  while  some  of  the  pressure 
is  due  to  the  expansion  of  gas  in  the  tree  by  the  rise  of  temperature,  this 
cannot  account  for  the  enormous  pressures  which  are  often  present,  for  ex- 
ample, when  after  a  rise  in  the  temperature  of  2°  C.  there  was  an  increase 
of  20  Ibs.  pressure. 

Then  again,  after  the  cessation  of  the  flow  in  late  spring  there  are  often  as 
great  differences  between  night  and  day  temperatures.  It  therefore 
seems  reasonable  to  conclude  that  the  expansion  of  gases  by  a  rise  in  tem- 
perature is  not  the  direct  cause. 

Activities  of  the  cells. — It  has  been  suggested  by  some  that  the  rise  in 
temperature  exercises  an  influence  on  the  protoplasts,  or  living  cells,  so 
that  they  are  stimulated  to  a  special  activity  resulting  in  an  exudation  pres- 
sure from  the  individual  cells,  which  is  known  to  take  place.  With  the  fall  of 


PATH  OF  MOVEMENTS.  55 

temperature  at  night  this  activity  would  cease  and  there  might  result  a 
lessened  pressure  in  the  cells.  Since  the  specific  activities  of  cells  are 
known  to  vary  in  different  plants,  and  in  the  same  plant  at  different 
seasons,  some  support  is  gained  for  this  theory,  though  it  is  generally 
believed  that  the  activities  of  the  living  cells  in  the  stems  are  not  necessary 
for  the  upward  flow  of  water.  It  must  be  admitted,  however,  that  at 
present  we  know  very  little  about  this  interesting  problem. 


CHAPTER  VI. 

MECHANICAL    USES    OF   WATER. 

111.  Turgidity  of  plant  parts.— As  we  have  seen  by  the 
experiments  on  the  leaves,  turgescence  of  the  cells  is  one  of  the 
conditions  which  enables  the  leaves  to  stand  out  from  the  stem, 
and  the  lamina  of  the  leaves  to  remain  in  an  expanded  position, 
so  that  they  are  better  exposed  to  the  light,  and  to  the  currents 
of  air.  Were  it  not  for  this  turgidity  the  leaves  would  hang 
down  close  against  the  stem. 

112.  Restoration  of  turgidity  in  shoots. — If  we  cut  off  a 
living  stem  of  geranium,  coleus,  tomato,  or  "  balsam,"  and  allow 
the  leaves  to  partly  wilt  so  that  the  shoot  loses  its 'turgidity,  it  is 
possible  for  this  shoot  to  regain  turgidity.  The  end  may  be 
freshly  cut  again,  placed  in  a  vessel  of  water,  covered  with  a  bell 
jar  and  kept  in  a  room  where  the  temperature 
is  suitable  for  the  growth  of  the  plant.  The 
shoot  will  usually  become  turgid  again  from 
the  water  which  is  absorbed  through  the  cut 
end  of  the  stem  and  is  carried  into  the  leaves 
where  the  individual  cells  become  turgid,  and 
the  leaves  are  again  expanded.  Such  shoots, 
and  the  excised  leaves  also,  may  often  be  made 
turgid  again  by  simply  immersing  them  in 
water,  as  one  of  the  experiments  with  the  salt 
solution  would  teach. 


Fig.  61. 

Restoration   of  turgidity 
(Sachs). 


113.  Turgidity  may  be  restored  more  certainly  and 
quickly  in  a  partially  wilted  shoot  in  another  way. 
The  cut  end  of  the  shoot  may  be  inserted  in  a  U  tube  as  shown  in  fig.  61,  the 
end  of  the  tube  around  the  stem  of  the  plant  being  made  air-tight.  The  arm 

56 


TURGESCENCE.  .  57 

of  the  tube  in  which  the  stem  is  inserted  is  filled  with  water  and  the  water  is 
allowed  to  partly  fill  the  other  arm.  Into  this  other  arm  is  then  poured 
mercury.  The  greater  weight  of  the  mercury  causes  such  pressure  upon  the 
water  that  it  is  pushed  into  the  stem,  where  it  passes  up  through  the  vessels 
in  the  stems  and  leaves,  and  is  brought  more  quickly  and  surely  to  the  cells 
which  contain  the  protoplasm  and  cell-sap,  so  that  turgidity  is  more  quickly 
and  certainly  attained. 

114.  Tissue  tensions. — Besides  the  turgescence  of  the  cells  of 
the  leaves  and  shoots  there  are  certain  tissue  tensions  without 
which  certain  tender  and  succulent  shoots,  etc.,  would  be  limp, 
and  would  droop.      There  are  a  number  of  plants  usually  accessi- 
ble, some  at  one  season  and  some  at  others,  which  may  be  used 
to  illustrate  tissue  tension. 

115.  Longitudinal  tissue  tension. — For  this  in  early  summer 
one   may   use  the   young  and   succulent   shoots   of  the   elder 
(sambucus);  or  the  petioles  of  rhubarb  during  the  summer  and 
early  autumn  ;  or  the  petioles  of  richardia.       Petioles  of  cala- 
dium  are  excellent  for  this  purpose,  and  these  may  be  had  at 
almost  any  season  of  the  year  from  the  greenhouses,   and  are 
thus   especially   advantageous  for  work  during  late  autumn  or 
winter.      The   tension  is   so   strong    that  a   portion  of  such  a 
petiole  io—i$cm  long  is  ample  to  demonstrate  it.     As  we  grasp 
the  lower  end  of  the  petiole  of  a  caladium,  or  rhubarb  leaf,  we 
observe  how  rigid  it  is,  and  how  well   it  supports    the  heavy- 
expanded  lamina  of  the  leaf. 

116.  The  ends  of  a  portion  of  such  a  petiole  or  other  object 
which  may  be  used  are  cut  off  squarely.      With  a  knife  a  strip 
from  2—^mm  in  thickness  is  removed  from  one  side  the  full 
length  of  the  object.     This  strip  we  now  find  is  shorter  than 
the   larger  part   from  which  it  was  removed.      The  outer  tissue 
then   exerts   a  tension  upon   the  petiole  which  tends  to  shorten 
it.      Let    us    remove    another   strip    lying    next    this    one,   and 
another,   and    so    on    until   the   outer  tissues  remain  only  upon 
one  side.     The  object  will  now  bend  toward  that  side.     Now 
remove   this    strip   and    compare    the    length    of  the  strips  re- 
moved with  the  central  portion.     We  find  that  they  are  much 


58  PHYSIOLOGY. 

shorter  now.  In  other  words  there  is  also  a  tension  in  the  tissue 
of  the  central  portion  of  the  petiole,  the  direction  of  which  is 
opposite  to  that  of  the  superficial  tissue.  The  parts  of  the  petiole 
now  are  not  rigid,  and  they  easily  bend.  These  two  longitudi- 
nal tissue  tensions  acting  in  opposition  to  each  other  therefore 
give  rigidity  to  the  succulent  shoot.  It  is  only  when  the  indi- 
vidual cells  of  such  shoots  or  petioles  are  turgid  that  these  tissue 
tensions  in  succulent  shoots  manifest  themselves  or  are  promi- 
nent. 

117.  To  demonstrate  the  efficiency  of  this  tension  in  giving  support,  let  us 
take  a  long  petiole  of  caladium  or  of  rhubarb.  Hold  it  by  one  end  in  a  hori- 
zontal position.  It  is  firm  and  rigid,  and  does  not  droop,  or  but  little.  Re- 
move all  of  the  outer  portion  of  the  tissues,  as  described  above,  leaving  only 
the  central  portion.  Now  attempt  to  hold  it  in  a  horizontal  position  by  one 
end.  It  is  flabby  and  droops  downward  because  the  longitudinal  tension  is 
removed. 

118.  Longitudinal  tension  in  dandelion  stems. — Take   long 

and  fresh  dandelion  stems.  Split 
them.  Note  that  they  coil.  The 
longitudinal  tension  is  very  great. 
Place  some  of  these  strips  in 
fresh  water.  They  coil  up  into 
close  curls  because  by  the  ab- 
sorption of  water  by  the  cells  the 
turgescence  of  the  individual  cells 
is  increased,  and  this  increases 
the  tension  in  the  stem.  Now 
place  them  in  salt  water  (a  5  per 
cent  solution).  Why  do  they 
uncoil  ? 

119.  To  imitate  the  coiling 
of  a  tendril. — Cut  out  a  narrow 
strip  from  a  long  dandelion  stem. 

Strip  from  dandelion  stem  made   to  Fasten   to   a   piece  of   soft   wood, 

with  the  ends  close  together,  as 

shown  in  fig.  62.  Now  place  it  in  fresh  water  and  watch  it  coil. 
Part  of  it  coils  one  way  and  part  another  way,  just  as  a  ten- 


MECHANICAL    USES  OF   WATER.  59 

dril  does  after  the  free  end  has  caught  hold  of  some  place  for 
support. 

120.  Transverse  tissue  tension.— To  illustrate  this  one  may 
take  a  willow  shoot  $-$cm  in  diameter  and  saw  off  sections  about 
2cm  long.  Cut  through  the  bark  on  one  side  and  peel  it  off  in  a* 
single  strip.  Now  attempt  to  replace  it.  The  bark  will  not 
quite  cover  the  wood  again,  since  the  ends  will  not  meet.  It 
must  then  have  been  held  in  transverse  tension  by  the  woody 
part  of  the  shoot. 


CHAPTER    VII. 

STARCH    AND   SUGAR    FORMATION 
1 .  The  Gases  Concerned. 

121.  Gas  given  off  by  green  plants  in  the  sunlight. — Let 

us  take  some  green  alga,  like  spirogyra,  which  is  in  a  fresh  con- 
dition, and  place  one  lot  in  a  beaker  or  tall  glass  vessel  of  water 
and  set  this  in  the  direct  sunlight  or  in  a  well  lighted  place.  At 
the  same  time  cover  a  similar  vessel 
of  spirogyra  with  black  cloth  so  that 
it  will  be  in  the  dark,  or  at  least  in 
very  weak  light. 

122.  In  a  short  time  we  note  that  in 
the  first  vessel  small  bubbles  of  gas  are 
accumulating    on    the    surface    of    the 
threads  of  the  spirogyra,  and  now  and 
then  some  free  themselves  and  rise  to 
the  surface  of  the  water.     Where  there 
is  quite  a  tangle  of  the  threads  the  gas 
is  apt  to  become  caught  and  held  back 
in  larger  bubbles,  which  on  agitation  of 
the  vessel  are  freed. 

If  we  now  examine  the  second  vessel  Oxygen  gas  given  off  by  spirogyra 
we  see  that  there  are  no  bubbles,  or  only  a  very  few  of  them. 
We  are  led  to  believe  then  that  sunlight  has  had  something  to 
do  with  the  setting  free  of  this  gas  from  the  plant. 

1230  We  may  now  take  another  alga  like  vaucheria  and  per- 
form the  experiment  in  the  same  way,  or  to  save  time  the 
two  may  be  set  up  at  once.  In  fact  if  we  take  any  of  the  green 

60 


STARCH  FORMATION:     THE   GASES.  6 1 

algae  and  treat  them  as  described  above  gas  will  be  given  off  in  a 
similar  manner. 

124.    We  may  now  take  one  of  the  higher  green  plants,  an 
aquatic  plant  like  elodea,   callitriche,  etc.      Place  the  plant  in 
the  water  with  the  cut  end  of  the  stem  uppermost, 
but  still  immersed,  the  plant  being  weighted  down 
by  a  glass  rod  or  other  suitable  object.      If  we 
place  the  vessel  of  water  containing  these   leafy 
stems  in  the  bright  sunlight,  in  a  short  time  bub- 
bles of  gas  will  pass  off  quite  rapidly  from  the  cut 
end  of  the  stem.      If  in    the    same  vessel  we 
place   another   stem,    from  which    the    leaves 
have  been  cut,  the  number  of  bubbles  of  gas 
KKi<  given  off  will  be  very  few.     This  indicates  that 

nubbles  of  oxygen  gas  ° 

given  off  from  elodea  in  a   large   part  of  the  gas  is    furnished   bv  the 

presence     of     sunlight.  * 

(°els->  leaves. 

125.  Another  vessel  fitted  up  in  the  same  way  should  be  placed  in  the 
dark  or  shaded  by  covering  with  a  box  or  black  cloth.     It  will  be  seen  here, 
as  in  the  case  of  spirogyra,  that  very  few  or  no  bubbles  of  gas  will  be  set 
free.     Sunlight  here  also  is  necessary  for  the  rapid  escape  of  the  gas. 

126.  We  may  easily  compare  the  rapidity  with  which  light  of  varying 
intensity  effects  the  setting  free  of  this  gas.     After  cutting  the  end  of  the  stem 
let  us  plunge  the  cut  surface  several  times  in  melted  paraffine,  or  spread 
over  the  cut  surface  a  coat  of  varnish.     Then  prick  with  a  needle  a  small 
hole   through  the  paraffine  or  varnish.     Immerse  the  plant  in  water  and 
place  in  sunlight  as  before.     The  gas  now  comes  from  the  puncture  through 
the  coating  of  the  cut  end,  and  the  number  of  bubbles  given  off  during  a 
given  period  can  be  ascertained  by  counting.     If  we  duplicate  this  experi- 
ment by  placing  one  plant  in  weak  light  or  diffused  sunlight,  and  another  m 
the  shade,  we  can  easily  compare  the  rapidity  of  the  escape  of  the  gas  under 
the  different  conditions,  which  represent  varying  intensities  of  light.     We 
see  then  that  not  only  is  sunlight  necessary  for  the  setting  free  of  this  gas,  but 
that  in  diffused  light  or  in  the  shade  the  activity  of  the  plant  in  this  respect 
is  less  than  in  direct  sunlight. 

127.  What  this  gas  is.  — If  we  take  quite  a  quantity  of  the 
plants   of  elodea   and  place  them    under   an    inverted    funnel 
which  is  immersed  in  water,  the  gas  will  be  given  off  in  quite  ' 
large  quantities  and  will  rise  into  the  narrow  exitot    the  funnel. 


62 


PHYSIOLOGY. 


The  funnel  should  be  one  with  a  short  tube,  or  the  vessel  one 
which  is  quite  deep  so  that  a  small  test  tube  which  is  filled  with 
water  may  in  this  condition  be  inverted  over  the 
opening  of  the  funnel  tube.  With  this  arrange- 
ment of  the  experiment  the  gas  will  rise  in  the 
inverted  test  tube,  slowly  displace  a  portion  of 
the  water,  and  become  collected  in  a  sufficient 
quantity  to  afford  us  a  test.  When  a  consider- 
able quantity  has  accumulated  in  the  test  tube,  we 
may  close  the  end  of  the  tube  in  the  water  with 
the  thumb,  lift  it  from  the  water  and  invert.  Flg-  6s" 

Apparatus   for  col- 

The  gas  will  rise   against   the  thumb.     A  dry  lectins   quantity    of 

J    oxygen   from  elodea. 

soft  pine  splinter  should  be  then  lighted,  and  (Detmer.) 
after  it  has  burned  a  short  time,  extinguish  the  flame  by  blowing 
upon  it,  when  the  still  burning  end  of  the  splinter  should  be 
brought  to  the  mouth  of  the  tube  as  the  thumb  is  quickly  moved 
to  one  side.  The  glowing  of  the  splinter  shows  that  the  gas  is 
oxygen. 

128.  It  is  better  to  allow  the  apparatus  to  stand  several  days 

in  the  sunlight  in  order  to 
catch  a  full  tube  of  the  gas. 
Or  on  a  sunny  day  carbon 
dioxide  gas  can  be  led  into 
the  water  in  the  jar  from 
a  generator,  such  an  one 


used    for  the   evolution  of 
The  CO2  can  be  produced 


as    is 
C02. 

by  the  action  of  hydrochloric  acid 
on  bits  of  marble.  The  CO2 
should  not  be  run  below  the  fun- 
nel. The  test-tube  should  be 
fastened  so  that  the  light  oxygen 
gas  will  not  raise  it  off  the  fun- 
nel. With  the  tube  full  of  gas  the 

Readytose7thTt\hegasis.   test   for  oxygen  can  be  made  by 
lifting  the  tube  with  one  hand  and 


Fig.  66. 


STARCH  FORMATION  — THE   GASES.  63 

quickly  thrusting  the  glowing  end  of  the  splinter  in  with  the 
other  hand.  If  properly 
handled,  the  splinter  will 
flame  again.  If  it  is  neces- 
sary to  keep  the  appa- 
ratus standing  for  more 

Fig.  67. 

than     one     day    it     is     Well        The  splinter  lights  again   in  the  presence  of 
i  i    f       *  -        .1        oxygen  gas. 

to  add  fresh  water  in   the 

place  of  most  of  the  water  in  the  jar.  Do  not  use  leaves  of  land 
plants  in  this  experiment,  since  the  bubbles  which  rise  when  these 
leaves  are  placed  in  water  are  not  evidence  that  this  process  is 
taking  place. 

129.  Oxygen  given  off  by  green  land  plants  also. — If  we  should  extend 
our  experiments  to  land  plants  we  should  find  that  oxygen  is  given  off  by 
them  under  these  conditions  of  light.     Land  plants,  however,  will  not  do 
this  when  they  are  immersed  in  water,  but  it  is  necessary  to  set  up  rather 
complicated  apparatus  and  to  make  analyses  of  the  gases  at  the  beginning 
and  at  the  close  of  the  experiments.     This  has  been  done,  however,  in  a  suffi- 
ciently large  number  of  cases  so  that  we  know  that  all  green  plants  in  the 
sunlight,  if  temperature  and  other  conditions  are  favorable,  give  off  oxygen. 

130.  Absorption  of  carbon  dioxide. — We  have  next  to  inquire 
where  the  oxygen  comes  from  which  is  given  off  by  green  plants 
when  exposed  to  the  sunlight,  and  also  to  learn  something  more 
of  the   conditions   necessary  for   the   process.     We   know   that 
water  which  has  been  for  some  time  exposed  to  the  air  and  soil, 
and  has  been  agitated,  like  running  water  of  streams,  or  the 
water  of  springs,  has  mixed  with  it  a  considerable  quantity  of 
oxygen  and  carbon  dioxide. 

If  we  boil  spring  water  or  hydrant  water  which  conies  from 
a  stream  containing  oxygen  and  carbon  dioxide,  for  about  20 
minutes,  these  gases  are  driven  off.  We  should  set  this  aside 
where  it  will  not  be  agitated,  until  it  has  cooled  sufficiently  to 
receive  plants  without  injury.  Let  us  now  place  some  spirogyra 
or  vaucheria,  and  elodea,  or  other  green  water  plant,  in  this 
boiled  water  and  set  the  vessel  in  the  bright  sunlight  under  the 
same  conditions  which  were  employed  in  the  experiments  for  the 
evolution  of  oxygen.  No  oxygen  is  given  off. 


64  PHYSIOLOGY. 

Can  it  be  that  this  is  because  the  oxygen  was  driven  from 
the  water  in  boiling?  We  shall  see.  Let  us  take  the  vessel 
containing  the  water,  or  some  other  boiled  water,  and  agitate  it 
so  that  the  air  will  be  thoroughly  mixed  with  it.  In  this  way 
oxygen  is  again  mixed  with,  the  water.  Now  place  the  plant 
again  in  the  water,  set  in  the  sunlight,  and  in  several  minutes 
observe  the  result.  No  oxygen  or  but  little  is  given  off.  There 
must  be  then  some  other  requisite  for  the  evolution  of  the  oxygen 

132.  The  gases  are  interchanged  in  the  plants. — We  will  now 
introduce  carbon  dioxide  again  in  the  water.     This  can  be  done 
by  leading  CO2  from  a  gas  generator  into  the  water.     Broken 
bits  of  marble  are  placed  in  the  generator,  acted  upon  by  hydro- 
chloric acid,  and  the  gas  is  led  over  by  glass  tubing.     Now  if  we 
place  the  plant  in  the  water  and  set  the  vessel  in  the  sunlight,  in 
a  few  minutes  the  oxygen  is  given  off  rapidly. 

133.  A  chemical  change  of  the  gas  takes  place  within  the 
plant  cell.— This  leads  us  to  believe  then  that  CO2  is  in  some 
way  necessary  for  the  plant  in  this  process.     Since  oxygen  is 
given  off  while  carbon  dioxide,  a  different  gas,  is  necessary,  it 
would  seem  that  a  chemical  change  takes  place  in  the  gases 
within  the  plant.     Since  the  process  takes  place  in  such  simple 
plants  as  spirogyra  as  well  as  in  the  more  bulky  and  higher 
plants,  it  appears  that  the  changes  go  on  within  the  cell,  in  fact 
within  the  protoplasm. 

134.  Gases  as  well  as  water  can  diffuse  through  the  proto- 
plasmic membrane. — Carbon  dioxide  then  is  absorbed  by  the 
plant  while  oxygen  is  given  off.     We  see  therefore  that  gases  as 
well  as  water  can  diffuse  through  the  protoplasmic  membrane  of 
plants  under  certain  conditions. 

2.  Where  Starch   is   Formed. 

We  have  found  by  these  simple  experiments  that  some 
chemical  change  takes  place  within  the  protoplasm  of  the  green 
cells  of  plants  during  the  absorption  of  carbon  dioxide  and  the 
giving  off  of  oxygen.  We  should  examine  some  of  the  green 
parts  of  those  plants  used  in  the  experiments,  or  if  they  are  not 


STARCH:    PHOTOSYNTHESIS.  65 

at  hand  we  should  set  up  others  in  order  to  make  this  examina- 
tion. 

135.  Starch  formed  as  a  result  of  this  process. — We  may  take 
spirogyra  which  has  been  standing  in  water  in  the  bright  sun- 
light for  several  hours.     A  few  of  the  threads  should  be  placed 
in  alcohol  for  a  short  time  to  kill  the  protoplasm.     From  the 
alcohol  we  transfer  the  threads  to  a  solution  of  iodine  in  potas- 
sium iodide.     We  find  that  at  certain  points  in  the  chlorophyll 
band  a  bluish  tinge,  or  color,  is  imparted  to  the  ring  or  sphere 
which  surrounds  the  pyrenoid.     In  our  first  study  of  the  spirogyra 
cell  we  noted  this  sphere  as  being  composed  of  numerous  small 
grains  of  starch  which  surround  the  pyrenoid. 

136.  Iodine  used  as  a  test  for  starch. — This  color  reaction 
which  we  have  obtained  in  treating  the  threads  with  iodine  is 
the  well-known  reaction,  or  test,  for  starch.     We  have  demon- 
strated then  that  starch  is  present  in  spirogyra  threads  which 
have  stood  in  the  sunlight  with  free  access  to  carbon  dioxide. 

If  we  examine  in  the  same  way  some  threads  which  have  stood 
in  the  dark  for  a  few  days  we  obtain  no  reaction  for  starch,  or  at 
best  only  a  slight  reaction.  This  gives  us  some  evidence  that  a 
chemical  change  does  take  place  during  this  process  (absorption 
of  CO2  and  giving  off  of  oxygen),  and  that  starch  is  a  product  of 
that  chemical  change. 

137.  Schimper's  method  of  testing  for  the  presence  of  starch. 
— Another  convenient  and  quick  method  of  testing  for  the  pres- 
ence  of   starch   is   what   is   known   as   Schimper's   method.     A 
strong  solution  of  chloral  hydrate  is  made  by  taking  8  grams  of 
chloral  hydrate  for  every  $cc  of  water.     To  this  solution  is  added 
a  little  of  an  alcoholic  tincture  of  iodine.     The  threads  of  spi- 
rogyra may  be   placed  directly  in  this  solution,  and  in  a  few 
moments  mounted  in  water  on  the  glass  slip  and  examined  with 
the  microscope.     The  reaction  is  strong  and  easily  seen. 

We  should  also  examine  the  leaves  of  elodea,  or  one  of 
the  higher  green  plants  which  has  been  for  some  time  in  the 
sunlight.  We  may  use  here  Schimper's  method  by  placing  the 
leaves  directly  in  the  solution  of  chloral  hydrate  and  iodine. 


66 


PHYSIO  LOG  Y. 


The  leaves  are  made  transparent  by  the  chloral  hydrate  so  that 
the  starch  reaction  from  the  iodine  is  easily  detected. 

The  following  is  a  convenient  and  safe  method  of  extract- 
ing chlorophyll  from  leaves.  Fill  a  large  pan,  preferably  a 
dishpan,  half  full  of  hot  water.  This  may  be  kept  hot  by  a 
small  flame.  On  the  water  float  an  evaporating  dish  partly 
filled  with  alcohol.  The  leaves  should  be  first  immersed  in 
the  hot  water  for  several  minutes,  then  placed  in  the  alcohol, 
which  will  quickly  remove  the  chlorophyll.  Now  immerse  the 
leaves  in  the  iodine  solution. 

138.  Green  parts  of  plants  form  starch  when  exposed  to 
light. — Thus  we  find  that  in  the  case  of  all  the  green  plants  we 
have  examined,  starch  is  present  in  the  green  cells  of  those  which 


Fig.  68.  Fig.  69. 

Leaf  of  coleus  showing  green  and  white     Similar  leaf  treated  with  iodine,  the  starch 
areas,  before  treatment  with  iodine.  reaction  only    showing  where  the    leaf 

was  green. 

have  been  standing  for  some  time  in  the  sunlight  where  the  proc- 
ess of  the  absorption  of  CO2  and  the  giving  off  of  oxygen  can 
go  on,  and  that  in  the  case  of  plants  grown  in  the  dark,  or  in 


STARCH  AND   SUGAR:     CHLOROPHYLL.  67 

leaves  of  plants  which  have  stood  for  some  time  in  the  dark, 
starch  is  absent.  We  reason  from  this  that  starch  is  the  product 
of  the  chemical  change  which  takes  place  in  the  green  cells 
under  these  conditions.  The  CO2  which  is  absorbed  by  the 
plant  mixes  with  the  water  (H2O)  in  the  cell  and  immediately 
forms  carbonic  acid.  The  chlorophyll  in  the  leaf  absorbs  radi- 
ant energy  from  the  sun  which  splits  up  the  carbonic  acid,  and 
its  elements  then  are  put  together  into  a  more  complex  com- 
pound, starch.  This  process  of  putting  together  the  elements 
of  an  organic  compound  is  a  synthesis,  or  a  synthetic  assimila- 
tion, since  it  is  done  by  the  living  plant.  It  is  therefore  a  syn- 
thetic assimilation  of  carbon  dioxide.  Since  the  sunlight  sup- 
plies the  energy  it  is  also  called  photosynthesis,  or  photo  synthetic 
assimilation.  We  can  also  say  carbon  dioxide  assimilation,  or 
CO2  assimilation  (see  paragraph  on  assimilation  at  close  of 
Chapter  10). 

139.  Starch  is  formed  only  in  the  green  parts  of  variegated 
leaves. — If  we  test  for  starch  in  variegated  leaves  like  the  leaf  of 
a  coleus  plant,  we  shall  have  an  interesting  demonstration  of  the 
fact  that  the  green  parts  of  plants  only  form  starch.     We  may 
take  a  leaf  which  is  partly  green  and  partly  white,  from  a  plant 
which  has  been  standing  for  some  time  in  bright  light.     Fig.  68 
is  from  a  photograph  of  such  a  leaf.     We  should  first  boil  jt  in 
alcohol  to  remove   the  green   color.     Now  immerse  it  in  the 
potassium  iodide  of  iodine  solution  for  a  short  time      The  parts 
which  were  formerly  green  are  now  dark  blue  or  nearly  black, 
showing  the  presence  of  starch  in  those  portions  of  the  leaf, 
while  the  white  part  of  the  leaf  is  still  uncolored.     This  is  well 
shown  in  fig.  69,  which  is  from  a  photograph  of  another  coleus 
leaf  treated  with  the  iodine  solution. 

3.  Chlorophyll  and  the  Formation  of  Starch. 

140.  In  our  experiments  thus  far  in  treating  of  the  absorption 
of  carbon  dioxide  and  the  evolution  of  oxygen,  with  the  accom- 
panying formation  of  starch,  we  have  used  green  plants. 


68  PHYSfOLOG  Y. 

141.  Fungi  cannot  form  starch. — If  we  should  extend  our 
experiments  to  the  fungi,  which  lack  the  green  color  so  charac- 
teristic of  the  majority  of  plants,  we  should  find  that  photosyn- 
thesis does  not  take  place  even  though  the  plants  are  exposed 
to  direct  sunlight.     These  plants  cannot  then  form  starch,  but 
obtain  carbohydrates  for  food  from  other  sources. 

142.  Photosynthesis  cannot  take  place  in  etiolated  plants. — 
Moreover  photosynthesis  is  usually  confined  to  the  green  plants, 
and  if  by  any  means  one  of  the  ordinary  green  plants  loses  its 
green  color  this  process  cannot  take  place  in  that  plant,  even 
when  brought  into  the  sunlight,  until  the  green  color  has  ap- 
peared under  the  influence  of  light. 

This  may  be  very  easily  demonstrated  by  growing  seedlings 
of  the  bean,  squash,  corn,  pea,  etc.  (pine  seedling?  are  green  even 
when  grown  in  the  dark),  in  a  dark  room,  or  in  a  dark  receiver 
of  some  kind  which  will  shut  out  the  rays  of  light.  The  room 
or  receiver  must  be  quite  dark.  As  the  seedlings  are  "coming 
up,"  and  as  long  as  they  remain  in  the  dark  chamber,  they  will 
present  some  other  color  than  green;  usually  they  are  somewhat 
yellowed.  Such  plants  are  said  to  be  etiolated.  If  they  are 
brought  into  the  sunlight  now  for  a  few  hours  and  then  tested 
for  the  presence  of  starch  the  result  will  be  negative.  But  if  the 
plant  is  left  in  the  light,  in  a  few  days  the  leaves  begin  to  take 
on  a  green  color,  and  then  we  find  that  carbon  dioxide  assimila- 
tion begins. 

143.  Chlorophyll  and  chloroplasts. — The  green  substance  in 
plants  is  then  one  of  the  important  factors  in  this  complicated 
process  of  forming  starch.      This  green  substance  is  chlorophyll, 
and  it  usually  occurs  in  definite  bodies,  the  chlorophyll  bodies, 
or  chloroplasts. 

The  material  for  new  growth  of  plants  grown  in  the  dark  is  derived  from 
the  seed.  Plants  grown  in  the  dark  consist  largely  of  water  and  protoplasm, 
the  walls  being  very  thin. 

144.  Form  of  the  chlorophyll  bodies. — Chlorophyll  bodies 
vary  in  form  in  some  different  plants,  especially  in  some  of  the 


STARCH  AND    SUGAR:    CHLOROPHYLL.  69 

lower  plants.  This  we  have  already  seen  in  the  case  of 
spirogyra,  where  the  chlorophyll  body  is  in  the  form  of  a  very 
irregular  band,  which  courses  around  the  inner  side  of  the  cell 
wall  in  a  spiral  manner.  In  zygnema,  which  is  related  to 
spirogyra,  the  chlorophyll  bodies  are  star-shaped.  In  the 
desmids  the  form  varies  greatly.  In  oedogonium,  another  of 
the  thread-like  algae,  illustrated  in  fig.  144,  the  chlorophyll  bodies 


Fig.  6ga. 

Section  of  ivy  leaf,  palisade  cells  above,  loose  parenchyma,  with  large  intercellular  spaces 
in  center.  Epidermal  cells  on  either  edge,  with  no  chlorophyll  bodies. 

are  more  or  less  flattened  oval  disks.  In  vaucheria,  too,  a 
branched  thread-like  alga  shown  in  fig.  138,  the  chlorophyll 
bodies  are  oval  in  outline.  .  These  two  plants,  cedogonium  and 
vaucheria,  should  be  examined  here  if  possible,  in  order  to  be- 
come familiar  with  their  form,  since  they  will  be  studied  later 
under  morphology  (see  chapters  on  adogonium  and  vaucheria, 
for  the  occurrence  and  form  of  these  plants).  The  form  of  the 
chlorophyll  body  found  in  oedogonium  and  vaucheria  is  that 
which  is  common  to  many  of  the  green  algae,  and  aLo  occurs  in 
the  mosses,  liverworts,  ferns,  and  the  higher  plants.  It  is  a 
more  or  less  rounded,  oval,  flattened  body. 

145.  Chlorophyll  is  a  pigment  which  resides  in  the  chloroplast. — That 
the  chlorophyll  is  a  coloring  substance  which  resides  in  the  chloroplastid, 
and  does  not  form  the  body  itself,  can  be  demonstrated  by  dissolving  out  the 
chlorophyll  when  the  framework  of  the  chloroplastid  is  apparent.  The 
green  parts  of  plants  which  have  been  placed  for  some  time  in  alcohol  lose 


7°  PHYSIOLOGY. 

their  green  color.  The  alcohol  at  the  same  time  becomes  tinged  with  green. 
In  sectioning  such  plant  tissue  we  find  that  the  chlorophyll  bodies,  or  chloro- 
plastids  as  they  are  more  properly  called,  are  still  intact,  though  the  green 
color  is  absent.  From  this  we  know  that  chlorophyll  is  a  substance  distinct 
from  that  of  the  chloroplastid. 

146.  Chlorophyll  absorbs  energy  from  sunlight  for  photosynthesis.  —It 
has  been  found  by  analysis  with  the  spectroscope  that  chlorophyll  absorbs  cer- 
tain of  the  rays  of  the  sunlight.     The  energy  which  is  thus  obtained  from 
the  sun,  called  kinetic  energy,  acts  on  the  molecules  of  CH2O3 ,  separating 
them  into  molecules  of  C,  H,  and  O.     (When  the  CO2  from  the  air  enters 
the  plant  cell  it  immediately  unites  with  some  of  the  water,  forming  carbonic 
acid  =  CH2O3.)     After  a  series  of  complicated  chemical  changes  starch  is 
formed  by  the  union  cf  carbon,  oxygen,  and  hydrogen.     In  this  process  of 
the  reduction  of  the  CH0O3  and  the  formation  of  starch  there  is  a  surplus  of 
oxygen,  which  accounts  for  the  giving  off  of  oxygen  during  the  process. 

147.  Kays  of  light  concerned    iu    phoiosyiicnesis. — If  a  solution  of 
chlorophyll  be  made,  and  light  be  passed  through   it,    and  this   light   be 
examined  with  the  spectroscope,  there  appear  what  are  called  absorption  bands. 
These    are  dark  bands  which  lie  across  certain  portions  of  the  spectrum. 
These  bands  lie  in  the  red,  orange,  yellow,  green,  blue,  and  violet,  but  the 
Lands  are  stronger  in  the  red,  which  shows  that  chlorophyll  absorbs  more  of 
the  red  rays  of  light  than  of  the  other  rays.     These  are  the  rays  of  low 
refrangibility.     The  kinetic  energy  derived  by  the  absorption  of  these  rays 
of  light   is  transformed  into  potential  energy.     That  is,  the  molecule  of 
CH2O3  is  broken  up,  and  then  by  a  different  combination  of  certain  elements 
starch  is  formed.* 

148.  Starch  grains  formed  in  the  chloroplasts. — During  photosynthesis  the 
starch  formed  is  deposited  generally  in  small  grains  within  the  green  chloro- 
plast  in  the  leaf.     We  can  see  this  easily  by  examining  the  leaves  of  some 
moss  like  funaria  which  has  been  in  the  light,  or  in  the  chloroplasts  of  the 
prothallia  of  ferns,  etc.     Starch  grains  may  also  be  formed  in  the  chloro- 
plasts from  starch  which  was  formed  in  some  other  part  of  the  plant,  but 


*  In  the  formation  of  starch  during  photosynthesis  the  separated  mole- 
cules fvom  the  carbon  dioxide  and  water  unite  in  such  a  way  that  carbon, 
hydrogen,  and  oxygen  are  united  into  a  molecule  of  starch.  This  result  is 
usually  represented  by  the  following  equation:  CO2+H2O  =  CH2O  +  O2. 
Then  by  polymerization  6(CH2O)  =  C6H12O8  =  grape  sugar.  Then 
C6H,2O6  —  H2O  =  CeHj.C^  =  starch.  It  is  believed,  however,  that  the 
process  is  much  more  complicated  than  this,  that  several  different  com- 
pounds are  formed  before  starch  finally  appears,  and  that  the  formula  for 
starch  is  much  higher  numerically  than  is  represented  by  C6H10O^. 


STARCH  AND   SUGAR;     CHLOROPHYLL.  ft 

which   has  passed  in  solution.     Thus  the  functions  of  the  chloroplast  are 
twofold,  that  of  photosynthesis  and  the  formation  of  starch  grains. 

149.  In  the  translocation  of  starch  when  it  becomes  stored  up  in  various 
parts  of  the  plant,  it  passes  from  the  state  of  solution  into  starch  grains  in 
connection  with  plastids  similar  to  the  chloroplasts,  but  which  are  not  green. 
The  green  ones  are  sometimes  called  chloroplasts,  while  the  colorless  ones 
are  termed  leucoplasts,  and  those  possessing  other  colors,  as  red  and  yellow? 
in  floral  leaves,  the  root  of  the  carrot,  etc.,  are  called  chromoplasts. 

150.  Photosynthesis  in  other  than  green  plants. — While  carbohydrates 
are  usually  only  formed  by  green  plants,  there  are  some  exceptions.     Ap- 
parent exceptions  are  found  in  the  blue-green  algae,  like  oscillatoria,  nostoc, 
or  in  the  brown  and  red  sea  weeds  like  fucus,  rhabdonia,  etc.     These  plants, 
however,  possess  chlorophyll,   but  it  is  disguised  by  another  pigment  or 
color.     There  are  plants,  however,  which  do  not  have  chlorophyll  and  yet 
form  carbohydrates  with  evolution  of  oxygen  in  the  presence  of  light,  as 
for  example  a  purple  bacterium,  in  which  the  purple  coloring  substance 
absorbs  light,  though  the  rays    absorbed  most  energetically  are  not  the 
red. 

151.  Influence  of  light  on  the  movement  of  chlorophyll  bodies. — In  fern 
prothallia. — If  we  place  fern  prothallia  in  weak  light  for  a  few  hours,  and 
then  examine  them  under  the  microscope,  we  find  that  the  most  of  the  chloro- 
phyll bodies  in  the  cells  are  arranged  along  the  inner  surface  of  the  hori- 
zontal wall.     If  now  the  same  prothallia  are  placed  in  a  brightly  lighted 
place  for  a  short  time  most  of  the  chlorophyll  bodies  move  so  that  they  are 


Fig.  70.  Fig.  71. 

Cell  exposed  to  weak  diffused  light  Same  cell  exposed  to  strong  light, 

showing  chlorophyll  bodies  along  the          showing      chlorophyll      bodies      have 
horizontal  walls.  moved  to  perpendicular  walls. 

Figs.  70,  71. — Cell  of  pro  thallium  of  fern. 


arranged  along  the  surfaces  of  the  perpendicular  walls,  and  instead  of  hav- 
ing the  flattened  surfaces  exposed  to  the  light  as  in  the  former  case,  the 
edges  of  the  chlorophyll  bodies  are  now  turned  toward  the  light.  (See  figs. 


72  PHYSIO  LOG  Y. 

70,  71.)  The  same  phenomenon  has  been  observed  in  many  plants.  Light 
then  has  an  influence  on  chlorophyll  bodies,  to  some  extent  determining 
their  position.  In  weak  light  they  are  arranged  so  that  the  flattened  sur- 
faces are  exposed  to  the  incidence  of  the  rays  of  light,  so  that  the  chloro- 
phyll will  absorb  as  great  an  amount  as  possible  of  kinetic  energy;  but 
intense  light  is  stronger  than  necessary,  and  the  chlorophyll  bodies  move  so 
that  their  edges  are  exposed  to  the  incidence  of  the  rays.  This  movement 
of  the  chlorophyll  bodies  is  different  from  that  which  takes  place  in  some 
water  plants  like  elodea  The  chlorophyll  bodies  in  elodea  are  free  in  the 
protoplasm.  The  protoplasm  in  the  cells  of  elodea  streams  around  the 
inside  of  the  cell  wall  much  as  it  does  in  nitella  and  the  chlorophyll  bodies 
are  carried  along  in  the  currents,  while  in  nitella  they  are  stationary. 


CHAPTER  VIII. 

STARCH  AND  SUGAR  CONCLUDED.  ANALYSIS  OF 
PLANT  SUBSTANCE. 

1 .  Translocation  of  Starch. 

152.  Translocation  of  starch.— It  has  been  found  that  leaves  of  many 
plants  grown  in  the  sunlight  contain  starch  when  examined  after  being  in 
the  sunlight  for  several  hours.  But  when  the  plants  are  left  in  the  dark  for 
a  day  or  two  the  leaves  contain  no  starch,  or  a  much  smaller  amount.  This 
suggests  that  starch  after  it  has  been  formed  may  be  transferred  from  the 
leaves,  or  from  those  areas  of  the  leaves  where  it  has  been  formed. 

To  test  this  let  us  perform  an  experiment  which  is  often  made.  We 
may  take  a  plant  such  as  a 
garden  tropaeolum  or  a  clover 
plant,  or  other  land  plant  in 
which  it  is  easy  to  test  for  the 
presence  of  starch.  Pin  a 
piece  of  circular  cork,  which 
is  smaller  than  the  area  of 
the  leaf,  on  either  side  of  the 
leaf,  as  in  fig.  72,  but  allow 

free  circulation  of  air  between  Fis-  ?2-  Fig.  73- 

.  Leaf  of  tropseomm  Leaf  ot  tropaeolum  treated 

the  cork  and  the  under  side  of  wjth  portion  covered  with  iodine  after  removal  of 

tlio     1*»Qf         Plarp     tV»f>     nlnnt  witn   c°rks  to    pre-  cork,  to  show  that  starch  is 

Flace    the    plant  vent  the  formation  removed  from  the  leaf  dur- 

where  it  will  be  in  the  sunlight,   of    starch.      (After    ing  the  night. 
On  the  afternoon  of  the  fol- 
lowing day,  if  the  sun  has  been  shining,  test  the  entire  leaf  for  starch.    The 
part  covered  by  the  cork  will  not  give  the  reaction  for  starch,  as  shown  by 
the  absence  of  the  bluish  color,  while  the  other  parts  of  the  leaf  will  show  it. 
The  starch  which  was  in  that  part  of  the  leaf  the  day  before  was  dissolved 
and  removed  during  the  night,  and  then  during   the   following  day,  the 
parts  being  covered  from  the  light,  no  starch  was  formed  in  them. 

73 


74  PHYSIO  LOG  Y. 

153.  Starch  in  other  parts  of  plants  than  the  leaves. — We 
may  use  the  iodine  test  to  search  for  starch  in  other  parts  of 
plants  than  the  leaves.     If  we  cut  a  potato  tuber,  scrape  some  of 
the  cut  surface  into  a  pulp,  and  apply  the  iodine  test,  we  obtain 
a  beautiful  and  distinct  reaction  showing  the  presence  of  starch. 
Now  we  have  learned  that  starch  is  only  formed  in  the  parts 
containing  chlorophyll.     We  have  also  learned  that  the  starch 
which  has  been  formed  in  the  leaves  disappears  from  the  leaf  or 
is  transferred  from  the  leaf.      We  judge  therefore  that  the  starch 
which  we  have  found  in  the  tuber  of  the  potato  was  formed  first 
in  the  green  leaves  of  the  plant,  as  a  result  of  photosynthesis. 
From  the  leaves  it  is  transferred  in  solution  to  the  underground 
stems,  and  stored  in  the  tubers.     The  starch  is  stored  here  by 
the  plant  to  provide  food  for  the  growth  of  new  plants  from  the 
tubers,   which   are   thus   much   more   vigorous   than   the  plants 
would  be  if  grown  from  the  seed. 

154.  Form  of  starch  grains. — Where  starch  is  stored  as  a  reserve  material 
it  occurs  in  grains  which  usually  have  certain  characters  peculiar  to  the 
species  of  plant  in  which  they  are  found.     They  vary  in  size  in  many 
Different  plants,  and  to  some  extent  in  form   also.     If  we    scrape    some   of 
the  cut  surface  of  the   potato    tuber  into  a  pulp  and  mount  a  small  quantity 
in    water,    or   make    a  thin    section    for   microscopic    examination,    \ve    find 
large   starch    grains   of  a   beautiful    structure.       The    grains    are   oval   in 
form  and  more  or  less  irregular  in  outline.     But  the  striking  peculiarity  is 
the  presence  of  what  seem  to  be  alternating  dark  and  light  lines  in  the  starch 
grain.     We  note  that  the  lines  form  irregular   rings,  which    are    smaller 
and  smaller  until  we  come  to  the  small  central  spot  termed  the  "  hilum  "  of 
the   starch  grain.     It  is  supposed  that  these  apparent  lines  in  the  starch 
grain  are  caused  by  the  starch  substance  being  deposited  in  alternating  dense 
and  dilute  layers,  the  dilute  layers  containing  more  water  than  the  dense 
ones;  others  think  that  the  successive  layers  from  the  hilum  outward  are 
regularly  of  diminishing  density,  and  that  this  gives  the  appearance  of  alter- 
nating lines.     The  starch  formed  by  plants  is  one  of  the  organic  substances 
which  are  manufactured  by  plants,  and  it  (or  glucose)  is  the  basis  for  the 
formation  of  other  organic  substances  in  the  plant.     Without  such  organic 
substances  green  plants  cannot  make  any  appreciable  increase  of  plant 
substance,  though  a  considerable  increase  in  size  of  the  plant  may  take 
place. 

NOTE. — The  organic  compounds  resulting  from  photosynthesis,  since 
they  are  formed  by  the  union  of  carbon,  hydrogen,  and  oxygen  in  such  a 
way  that  the  hydrogen  and  oxygen  are  usually  present  in  the  same  propor- 


STARCH:    TRAtfSLOCATIOX.  75 

tion  as  in  water,  are  called  carbohydrates.  The  most  common  carbo- 
hydrates are  sugars  (cane  sugar,  C12H22On,  for  example,  in  beet  roots, 
sugar  cane,  sugar  maple,  etc.),  starch,  and  cellulose. 

155.  Vaucheiia. — The    result    of    carbon   dioxide    assimilation    in    the 
threads  of  Vaucheria  is  not  clearly  understood.     Starch  is  absent  or  diffi- 
cult to  find  in  all  except  a  few  species,  while  oil  globules  are  present  in 
most   species.     These   oil   globules   are   spherical,    colorless,    globose    and 
highly  refringent.     Often  small  ones   are   seen  lying  against  chlorophyll 
bodies.     Oil  is  a  hydrocarbon  (containing  C,  H,  and  O,  but  the  H  and  O 
are  in  different  proportions  from  what  they  are  in  H2O)  and  until  recently 
it  was  supposed  that  this  oil  in  Vaucheria  was  the  direct  result  of  photo- 
synthesis.    But  the  oil  does  not  disappear  when  the  plant  is  kept  for  a 
long  time  in  the  dark,  which  seems  to  show  that  it  is  not  the  direct  prod- 
uct of  carbon  dioxide  assimilation,  and  indicates  that  it  comes  either  from 
a  temporary  starch  body  or  from  glucose.     Schimper  found  glucose  in  sev- 
eral species  of  Vaucheria,  and  Waltz  says  that  some  starch  is  present  in 
Vaucheria  sericea,  while  in  V.  tuberosa  starch  is  abundant  and  replaces  the 
oil.     To  test  for  oil  bodies  in  Vaucheria  treat  the  threads  with  weak  osmic 
acid,  or  allow  them  to  stand  for  twenty-four  hours  in  Fleming's  solution 
(which   contains  osmic  acid).     Mount  some  threads  and  examine  with 
microscope.     The  oil  globules  are  stained  black. 

2.  Sugar,  and  Digestion  of  Starch.* 

156.  The  sugar  produced  as  the  result  of  photosynthesis  may  be  stored 
as  sugar  or  changed  to  starch.     In  general  sugar  is  more  common  in  the 
green  parts  of  monocotyledonous  plants,  while  starch  is  most  frequent  in 
dicotyledons.     Plant  sugars  are  of  three  general  kinds:  cane  sugar  or  sucrose, 
abundant  in  the  sugar  cane,   sugar  beet,   sugar  maple,   etc.;    glucose  or 
fruit  sugar,  found  in  the  fruit  of  a  majority  of  plants,  and  abundant  in  some, 
as  in  apples,  pears,  grapes,  etc.  (in  many  fruits  and  other  parts  of  plants 
both  glucose  and  cane  sugar  are  present);  and  maltose,  as  in  malted  barley. 

157a.  Test  for  sugars. — Make  a  weak  solution  of  pure  commercial 
grape  sugar  (glucose)  and  also  one  of  pure  granulated  cane  sugar.  Partly 
fill  two  test  tubes  with  Fehling's  solution.!  To  one  add  some  of  the  grape- 
sugar  solution  and  to  the  other  add  some  of  the  cane-sugar  solution.  After 
these  tubes  have  stood  in  a  warm  place  a  few  hours,  it  will  be  found  that 
a  bright  orange-brown  or  cinnabar-colored  precipitate  of  copper  and  cuprous 
oxide  has  formed  in  the  tube  containing  grape  sugar,  while  the  other  solu- 
tion is  unchanged.  Grape  sugar  or  glucose  therefore  reduces  Fehling's 
solution,  while  cane  sugar  as  such  has  no  effect  upon  it. 

1576.  Test  for  cane  sugar.— Place  a  small  quantity  of  pure  granulated 
cane  sugar  in  a  test  tube  and  add  about  15  cc.  of  distilled  water.  To 

*  Paragraphs  156-160  were  prepared  by  Dr.  E.  J.  Durand. 

*  See  page  712  for  formula  for  Fehling's  solution. 


76  PHYSIOLOGY. 

this  add  i  to  2  cc.  of  cobaltous  nitrate  solution  (5  grams  cobalt  nitrate  in  100 
cc.  distilled  water.  Keep  in  a  stoppered  bottle),  then  add  a  small  quantity 
of  a  strong  sodium  hydrate  solution  (50  grams  caustic  soda,  in  sticks,  to 
100  cc.  distilled  water.  Keep  in  a  bottle).  A  beautiful  violet  color  appears. 
Test  glucose  or  grape  sugar  in  the  same  way  and  a  blue  color  appears, 
which  gradually  changes  to  green. 

157c.  Cane  sugar  (sucrose)  can  be  changed  to  glucose  or  invert  sugar 
in  the  following  way:  To  a  weak  solution  of  pure  granulated  cane  sugar 
in  a  small  beaker  add  a  few  drops  of  strong  hydrochloric  acid,  rest  on  gauze 
wire,  and  boil  for  a  minute  or  two  over  a  flame.  This  inverts  the  cane 
sugar  to  glucose  (equal  parts  of  dextrose  and  laevulose).  To  test  for  the 
invert  sugar  the  acid  must  be  neutralized.  Add  sodium  carbonate  until  on 
adding  no  effervescence  takes  place.  Now  add  the  Fehling's  solution  and 
boil;  the  red  precipitate  appears,  showing  that  it  reduces  Fehling's  solution. 

158a.  Tests  for  sugar  in  plant  tissue. — Scrape  out  a  little  of  the  tissue 
from  the  inside  of  a  ripe  apple  or  pear,  place  it  with  a  little  water  in  a  test 
tube,  and  add  a  few  drops  of  Fehling's  solution.  After  standing  half  an 
hour  the  characteristic  precipitate  of  copper  and  cuprous  oxide  appears, 
showing  that  grape  sugar  is  present  in  quantity. 

Make  thin  sections  of  the  apple  and  mount  in  a  drop  of  Fehling's  solution 
on  a  slide.  After  an  hour  examine  with  the  microscope.  The  granules 
of  cuprous  oxide  are  present  in  the  cells  of  the  tissue  in  great  abundance. 

1586.  Prepare  another  tube  with  some  of  the  pulp  in  15  cc.  of  water; 
add  2  cc.  of  cobaltous  nitrate  solution,  and  then  some  of  the  strong  sodium 
hydrate  solution,  as  in  paragraph  157^.  Cane  sugar  as  well  as  grape 
sugar  is  present  in  these  fruits. 

158c.  Cut  up  several  leaves  of  a  vigorous  young  Indian  corn  seedling 
in  a  small  beaker  and  add  25  or  30  cc.  distilled  water.  Boil  for  one  or 
two  minutes.  Filter.  In  another  small  beaker  boil  Fehling's  solution, 
and  if  it  is  free  from  sediment  (if  not,  filter)  add  a  portion  of  the  filtered 
corn -leaf  solution  and  boil  for  two  minutes.  Hold  the  beaker  toward  the 
light  and  look  on  the  bottom  for  the  red  precipitate.  Filter.  The  red 
precipitate  shows  the  presence  of  glucose  (or  invert  sugar).  Take  the 
remaining  portion  of  the  corn-leaf  decoction  in  a  test  tube  and  test  for  cane 
sugar  by  adding  cobaltous  nitrate  and  sodium  hydrate  as  in  paragraph 
1576.  If  the  violet  color  does  not  appear  at  once,  do  not  agitate  it,  but 
allow  it  to  stand  for  a  while.  The  violet  color  appears  at  the  bottom  of  the 
tube,  showing  the  presence  of  cane  sugar,  while  the  reaction  for  glucose  may 
appear  in  the  upper  portion  of  the  solution.  For  comparison  take  similar 
corn  leaves,  remove  the  chlorophyll  with  alcohol,  and  test  with  iodine.  No 
starch  reaction  appears.  The  carbohydrate  in  corn  leaves  is  therefore  sugar 
and  not  starch.  If  now  the  grain  of  corn  be  examined  the  cells  will  be 
found  to  be  full  of  starch  grains,  which  give  the  beautiful  blue  reaction 


SUGAR:    DIGESTION   OF  STARCH.  77 

with  iodine.  This  experiment  shows  that  sugar  is  formed  in  the  leaves  of 
the  Indian  corn  plant,  but  is  changed  to  starch  when  stored  in  the  seed. 

158d.  Take  several  leaves  of  bean  seedlings;  test  for  glucose  and  cane 
sugar  as  in  158^.  Both  are  present.  Test  a  leaf  for  starch.  It  is  present. 

158e.  Select  a  branch  of  sugar  maple  during  autumn,  winter,  or  spring, 
about  i  cm.  in  diameter.  From  a  portion  scrape  off  all  the  bark  so  as 
to  remove  all  the  color.  Cut  off  some  shavings  of  the  white  woody  portion 
and  boil  in  a  small  beaker  for  one  or  two  minutes.  Filter  and  test  for  the 
presence  of  both  glucose  and  cane  sugar  as  in  paragraphs  158^  and  157^. 
Both  are  present  (at  least  in  several  testsmade  in  December,  1906).  The  bane 
is  to  be  removed,  since  the  coloring  matter  in  it  also  reduces  Fehling's  solution 

158/.  Scrape  some  pulp  from  the  inside  of  a  sugar  beet.  Mix  in  dis- 
tilled water  in  two  test  tubes.  Test  one  for  glucose  and  the  other  for  cane 
sugar.  Cane  sugar  is  present. 

159.  How  starch  is  changed  to  sugar.  —We  have  seen  that  in  many  plants 
the  carbohydrate  formed  as  the  result  of  carbon  dioxide  assimilation  is 
stored  as  starch.     This  substance  being  insoluble  in  water  must  be  changed 
to  sugar,  which  is  soluble  before  it  can  be  used  as  food  or  transported  to 
other  parts  of  the  plant.     This  is  accomplished  through  the  action  of  cer- 
tain enzymes,  principallv  diastase.      This  substance  has  the  power  of  act- 
ing upon  starch  under  proper  conditions  of  temperature  and  moisture, 
causing  it  to  take  up  the  elements  of  water,  and  so  to  become  sugar. 

This  process  takes  place  commonly  in  the  leaves  where  starch  is  formed, 
but  especially  in  seeds,  tubers  (during  the  sprouting,  etc.),  and  other  parts 
which  the  plant  uses  as  storehouses  for  starch  food.  It  is  probable  that 
the  same  conditions  of  temperature  and  moisture  which  favor  germination 
or  active  growth  are  also  favorable  to  the  production  of  diastase. 

160.  Experiments  to  show  the  action  of  diastase. — (a)  Place  a  bit  of 
starch  half  as  large  as  a  pea  in  a  test  tube,  and  cover  with  a  weak  solution  * 
(about  \  per  cent)  of  commercial  taka  diastase.     After  it  has  stood  in  a 
warm  place  for  five  or  ten  minutes  test  with  Fehling's  solution.     The  pre- 
cipitate of  cuprous  oxide  appears  showing  that  some  of  the  starch  has  been 
changed  to  sugar.     By  using  measured  quantities,   and  by  testing  with 
iodine  at  frequent  intervals,  it  can  be  determined  just  how  long  it  takes  a 
given  quantity  of  diastase  to  change  a  known  quantity  of  starch.     In  this 
connection  one  should  first  test  a  portion  of  the  same  starch  with  Fehling's 
solution  to  show  that  no  sugar  is  present. 

(ft)  Repeat  the  above  experiment  using  a  little  tissue  from  a  potato,  and 
some  from  a  corn  seed. 

(c)  Take  25  germinating  barley  seeds  in  which  the  radicle  is  just  appear- 


*  This  solution  of  taka  diastase  should  be  made  up  cold.     If  it  is  heated 
to  60°  C.  or  over  it  is  destroyed. 


78  PHYSIOLOGY. 

ing.  Grind  up  thoroughly  in  a  mortar  with  about  three  parts  of  water. 
After  this  has  stood  for  ten  or  fifteen  minutes,  filter.  Fill  a  test  tube  one- 
third  full  of  water,  add  a  piece  of  starch  half  the  size  of  a  pea  or  less,  and 
boil  the  mixture  to  make  starch-paste.  Add  the  barley  extract.  Put  in  a 
warm  place  and  test  from  time  to  time  with  iodine.  The  first  samples  so 
treated  will  be  blue,  later  ones  violet,  brown,  and  finally  colorless,  showing 
that  the  starch  has  all  disappeared.  This  is  due  to  the  action  of  the  dias- 
tase which  was  present  in  the  germinating  seeds,  and  which  was  dissolved 
out  and  added  to  the  starch  mixture.  The  office  of  this  diastase  is  to 
change  the  starch  in  the  seeds  to  sugar.  Germinating  wheat  is  sweet,  and 
it  is  a  matter  of  common  observation  that  bread  made  from  sprouted  wheat 
is  sweet. 

(d)  Put  a  little  starch-paste  in  a  test  tube  and  cover  it  with  saliva  from 
the  mouth.  After  ten  or  fifteen  minutes  test  with  Fehling's  solution.  A 
strong  reaction  appears  showing  how  quickly  and  effectively  saliva  acts  in 
converting  starch  to  sugar.  Successive  tests  with  iodine  will  show  the 
gradual  disappearance  of  the  starch. 

161.  These  experiments  have  shown  us  that  diastase  from  three  different 
sources  can  act  upon  starch  converting  it  into  sugar.  The  active  principle 
in  the  saliva  is  an  animal  diastase  (ptyaliri),  which  is  necessary  as  one  step 
in  the  digestion  of  starch  food  in  animals.  The  taka  diastase  is  derived 
from  a  fungus  (Eurotium  oryzae)  which  feeds  on  the  starch  in  rice  grains 
converting  it  into  sugar  which  the  fungus  absorbs  for  food.  The  malt  dias- 
tase and  leaf  diastase  are  formed  by  the  seed  plants.  That  in  seeds  con- 
verts the  starch  to  sugar  which  is  absorbed  by  the  embryo  for  food.  That 
in  the  leaf  converts  the  starch  into  sugar  so  that  it  can  be  transported  to 
other  parts  of  the  plant  to  be  used  in  building  new  tissue,  or  to  be  stored 
again  in  the  form  of  starch  (example,  the  potato,  in  seeds,  etc.).  The 
starch  is  formed  in  the  leaf  during  the  daylight.  The  light  renders  the 
leaf  diastase  inactive.  But  at  night  the  leaf  diastase  becomes  active  and 
converts  the  starch  made  during  the  day.  Starch  is  not  soluble  in  water, 
while  the  sugar  is,  and  the  sugar  in  solution  is  thus  easily  transported 
throughout  the  plant.  In  those  green  plants  which  do  not  form  starch  in 
their  leaves  (sugar  beet,  corn,  and  many  monocotyledons),  grape  sugar 
and  fruit  sugar  are  formed  in  the  green  parts  as  the  result  of  photosynthesis. 
In  some,  like  the  corn,  the  grape  sugar  formed  in  the  leaves  is  transported 
to  other  parts  of  the  plant,  and  some  of  it  is  stored  up  in  the  seed  as  starch. 
In  others  like  the  sugar  beet  the  glucose  and  fruit  sugar  formed  in  the 
leaves  flow  to  other  parts  of  the  plant,  and  much  of  it  is  stored  up  as  cane 
sugar  in  the  beet  root.  The  process  of  photosynthesis  probably  proceeds 
in  the  same  way  in  all  cases  up  to  the  formation  of  the  grape  sugar  and 
fruit  sugar  in  the  leaves.  In  the  beet,  corn,  etc.,  the  process  stops  hera 
while  in  the  bean,  clover,  and  most  dicotyledons  the  process  is  carried  one 
step  farther  in  the  leaf  and  starch  is  *orm«d. 


ANALYSIS   OF  PLANT  SUBSTANCE.  79 

3.  Rough  Analysis  of  Plant  Substance. 

162.  Some  simple  experiments  to  indicate  the  nature  of  plant  substance. — 

After  these  building-up  processes  of  the  plant,  it  is  instructive  to  perform 
some  simple  experiments  which  indicate  roughly  the  nature  of  the  plant 
substance,  and  serve  to  show  how  it  can  be  separated  into  other  substances, 
some  of  them  being  reduced  to  the  form  in  which  they  existed  when  the 
plant  took  them  as  food.  For  exact  experiments  and  results  it  would  be 
necessary  to  make  chemical  analyses. 

163.  The  water  in  the  plant. — Take  fresh  leaves  or  leafy  shoots  or  other 
fresh  plant  parts.     Weigh.     Permit  them  to  remain  in  a  dry  room  until 
they  are  what  we  call  "dry."     Now  weigh.     The  plants  have  lost  weight, 
and  from  what  we  have  learned  in  studies  of  transpiration  this  loss  in  weight 
we  know  to  result  from  the  loss  of  water  from  the  plant. 

164.  The  dry  plant  material  contains  water. — Take  air-dry  leaves,  shav- 
ings, or  other  dry  parts  of  plants.     Place  them  in  a  test  tube.     With  a 
holder  rest  the  tube  in  a  nearly  horizontal  position,  with  the  bottom  of  the 
tube  in  the  flame  of  a  Bunsen  burner.     Very  soon,  before  the  plant  parts 
begin  to  "burn,"  note  that  moisture  is  accumulating  on  the  inner  sxirface 
of  the  test  tube.     This  is  water  driven  off  which  could  not  escape  by  drying 
in  air,  without  the  addition  of  artificial  heat,  and  is  called  "hygroscopic 
water." 

165.  Water  formed  on  burning  the  dry  plant  material. — Light  a  soft-pine 
or  bass-wood  splinter.     Hold  a  thistle  tube  in  one  hand  with  the  bulb  down- 
ward and  above  the  flame  of  the  splinter.     Carbon  will  be  deposited  over 
the  inner  surface  of  the  bulb.     After  a  time  hold  the  tube  toward  the  win- 
dow and  look  through  it  above  the  carbon.     Drops  of  water  have  accumu- 
lated on  the  inside  of  the  tube.     This  water  is  formed  by  the  rearrangement 
of  some  of  the  hydrogen  and  oxygen,  which  is  set  free  by  the  burning  of 
the  plant  material,  where  they  were  combined  with  carbon,  as  in  the  cellu- 
lose, and  with  other  elements. 

166.  Formation  of  charcoal  by  burning. — Take  dried  leaves,  and  shav- 
ings from  some  soft  wood.     Place  in  a  porcelain  crucible,  and  cover  about 
3  cm.  deep  with  dry  fine  earth.     Place  the  crucible  in  the  flame  of  a  Bun- 
sen  burner  and  let  it  remain  for  about  fifteen  minutes.     Remove  and  empty 
the  contents.     If  the  flame  was  hot  the  plant  material  will  be  reduced  to  a 
good  quality  of  charcoal.     The  charcoal  consists  largely  of  carbon. 

167.  The  ash  of  the  plant. — Place  in  the  porcelain  crucible  dried  leaves 
and  shavings  as  before.     Do  not  cover  with  earth.     Place  the  crucible  in 
the  flame  of  the  Bunsen  burner,  and  for  a  moment  place  on  the  porcelain 
cover;    then  remove  the  cover,  and  note  the  moisture  on  the  under  surface 
from  the  escaping  water.     Permit  the  plant  material  to  burn;   it  may  even 
flame  for  a  time.     In  the  course  of  fifteen  minutes  it  is  reduced  to  a  whitish 


80 


PHYSIO  LOG  y. 


powder,  much  smaller  in  bulk  than  the  charcoal  in  the  former  experiment. 
This  is  the  ash  of  the  plant. 

168.  What  has  become  of  the  carbon  ? — In  this  experiment    the  air   was 
not  excluded  from  the  plant  material,  so  that  oxygen  combined  with  carbon 
as  the  water  was  freed,  and  formed  carbon  dioxide,  passing  off  into  the  air 
in  this  form.     This  it  will  be  remembered  is  the  form  in  which  the  plant 
took  the  carbon-food  in  through  the  leaves.     Here  the  carbon  dioxide  met 
the  water  coming  from  the  soil,  and  the  two  united  to  form,  ultimately, 
starch,  cellulose,  and  other  compounds  of  carbon;    while  with  the  addition 
of  nitrogen,  sulphur,  etc.,  coming  also  from  the  soil,  still  other  plant  sub- 
stances were  formed. 

169.  The  carbohydrates    are  classed    among  the  non-nitrogenous    sub- 
stances.    Other  non-nitrogenous  plant  substances  are  the    organic  acids 
like  oxalic  acid  (H2C2O4),  malic  acid  (H2C4H4O5),  etc.;    the  fats  and  fixed 
oils,  which  occur  in  the  seeds  and  fruits  of  many  plants.     Of  the  nitrogenous 
substances  the  proteids  have  a  very  complex  chemical  formula  and  contain 
carbon,   hydrogen,   oxygen,   nitrogen,   sulphur,   etc.   (example,   aleuron,  or 
proteid  grains,  found  in  seeds).     The  proteids  are  the  source  of  nitrogenous 
food    for    the    seedling   during   germination.     Of   the    amides,    asparagin 
(C4H8N3O3)  is  an  example  of  a  nitrogenous  substance;   and  of  the  alkaloids, 
nicotin  (C;0H14N2)  from  tobacco. 

All  living  plants  contain  a  large  per  cent  of  water.  According  to  Vines 
"ripe  seeds  dried  in  the  air  contain  12  to  15  per  cent  of  water,  herbaceous 
plants  60  to  80  per  cent,  and  many  water-plants  and  fungi  as  much  as  95 
per  cent  of  their  weight."  When  heated  to  100°  C.  the  water  is  driven  off. 
The  dry  matter  remaining  is  made  up  partly  of  organic  compounds,  exam- 
ples of  which  are  given  above,  and  inorganic  compounds.  By  burning  this 
dry  residue  the  organic  substances  are  mostly  changed  into  volatile  prod- 
ucts, principally  carbonic  acid,  water,  and  nitrogen.  The  inorganic  sub- 
stances as  a  result  of  combustion  remain  as  a  white  or  gray  powder,  the  ash. 

The  amount  of  the  ash  increases  with  the  age  of  the  plant,  though  the 
percentage  of  ash  may  vary  at  different  times  in  the  different  members  of 
the  plant.     The  following  table  taken  from  Vines  will  give  an  idea  of  the 
amount  and  composition  of  the  ash  in  the  dry  solid  of  a  few  plants: 
CONTENT  OP  1000  PARTS  OF  DRY  SOLID  MATTER. 


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Wheat,  straw.  .  .  . 
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0.42 

Peas  (the  seed).  .  . 

CHAPTER   IX. 

HOW    PLANTS    OBTAIN    THEIR    FOOD.     I. 
1.  Sources  of  Plant  Food. 

170.  The  necessary  constituents  of  plant  food. — As  indicated  in  Chap- 
ter 3,  investigation  has  taught  us  the  principal  constituents  of  plant  food. 
Some  suggestion  as  to  the  food  substances  is  derived  by  a  chemical  analysis 
of  various  plants.    In  Chapter  8  it  was  noted  that  there  are  two  principal 
kinds  of  compounds  in  plant  substances,  the  organic  compounds  and  the 
inorganic  compounds  or  mineral  substances.     The  principal  elements  in 
the  organic  compounds  are  hydrogen,  carbon,  oxygen  and  nitrogen.     The 
elements  in  the  inorganic  compounds  which  have  been  found  indispensable 
to  plant  growth  are  calcium,*  potassium,  magnesium,  phosphorus,  sulphur 
and  iron.     (See  paragraphs  54-58,   and   complete  observations  on  water 
cultures.)     Other  elements  are  found  in  the  ash  of  plants;  and  while  they 
are  not  absolutely  necessary  for  growth,  some  f  of  them  are  beneficial  in 
one  way  or  another. 

171.  The  carbohydrates  are  derived,  as  we  have  learned,  from  the  CO2 
of  the  air,  and  water  in  the  plant  tissue  drawn  from  the  soil;   though  in  the 
case  of  aquatic  plants  entirely  submerged,  all  the  constituents  are  absorbed 
from  the  surrounding  water. 

172.  Food  substances  in  the  soil. — Land  plants  derive  their  mineral  food 
from  the  soil,  the  soil  received  the  mineral  substances  from  dissolving  and 
disintegrating  rocks.     Nitrogenous  food  is  chiefly  derived  from  the  same 
source,  but  under  a  variety  of  conditions  which  will  be  discussed  in  later 
paragraphs,  but  the  nitrogen  comes  primarily  from  the  air.     Some  of  the 
mineral  substances,  those  which  are  soluble  as  well  as  some  of  the  nitrog- 
enous substances,  are  found  in  solution  in  the  soil.      These   are  absorbed 
by  the  plant,  as  needed,  along  with  water,  through  the  root  hairs. 


*  Calcium  is  not  essential  for  the  growth  of  the  fungi, 
f  For  example,  silicon  is  used  by  some  plants  in  strengthening  supporting 
tissues.     Buckwheat  thrives  better  when  supplied  with  a  chloride. 

8l 


82  PHYSIOLOGY. 

173.  Absorption  of  soluble  substances. — Since  these  substances  are  dis- 
solved in  the  water  of  the  soil,  it  is  not  necessary  for  us  to  dwell  on  the 
process  of  absorption.  This  in  general  is  dwelt  upon  in  Chapter  3.  It 
should  be  noted,  however,  that  food  substances  in  solution,  during  absorp- 
tion, diffuse  through  the  protoplasmic  membrane  independently  of  each 
other  and  also  independently  of  the  rate  of  movement  of  the  water  from 
the  soil  into  the  root  hairs  and  cells  of  the  root. 

When  the  cells  have  absorbed  a  certain  amount  of  a  given  substance,  no 
more  is  absorbed  until  the  concentration  of  the  cell-sap  in  that  particular 
substance  is  reduced.  This,  however,  does  not  interfere  with  the  absorp- 
tion of  water,  or  of  other  substances  in  solution  by  the  same  cells.  Plants 
have  therefore  a  certain  selective  power  in  the  absorption  of  food  substances. 

174.  Action  of  root  hairs  on  insoluble  substances.   Acidity  of 
root  hairs. — If  we  take  a  seedling  which  has  been  grown  in  a 
germinator,  or  in  the  folds  of  cloths  or  paper,  so  that  the  roots  are 
free  from  the  soil,  and  touch  the  moist  root  hairs  to  blue  litmus 
paper,  the  paper  becomes  red  in  color  where  the  root  hairs  have 
come  in  contact.     This  is  the  reaction  for  the  presence  of  an  acid 
salt,  and  indicates  that  the  root  hairs  excrete  certain  acid  sub- 
stances.    This  acid  property  of  the  root  hairs  serves  a  very  im- 
portant function  in  the  preparation  of  certain  of  the  elements  of 
plant  food  in  the  soil.      Certain  of  the  chemical  compounds  of 
potash,  phosphoric  acid,  etc.,  become  deposited  on  the  soil  par- 
ticles, and  are  not  soluble  in  water.     The  acid  of  the  root  hairs 
dissolves  some  of  these  compounds  where  the  particles  of  soil  are 
in  close  contact  with  them,  and  the  solutions  can  then  be  taken  up 
by  the  roots.     Carbonic  acid  and  other  acids  are  also  formed  in 
the  soil,  and  aid  in  bringing  these  substances  into  solution. 

175.  This  corrosive  action  of  the  roots  can  be  shown  by  the  well-known 
experiment  of  growing  a  plant  on  a  marble  plate  which  is  covered  by  soil 
In  lieu*  of   the  marble  plate,  the  peas  may  be  planted  .in  clam  or  oyster 
shells,  which  are  then  buried  in  the  soil  of  the  pot,  so  that  the  roots  of  the 
seedlings  will  come  in  contact  with  the  smooth  surface  of  the  shell.     After 
a  few  weeks,  if  the  soil  be  washed  from  the  marble  where  the  roots  have 
been  in  close  contact,  there  will  be  an  outline  of  this  part  of:  the  root  sys- 
tem.    Several   different   acid   substances   are   excreted   from   the  roots   of 
plants  which  have  been  found  to  redden  blue  litmus  paper  by  contact 
Experiments  by  Czapek  show,  however,  that  the  carbonic  acid  excreted  by 
the  roots  has  the  power  of  directly  bringing  about  these  corrosion  phenom- 


PARASITES  AND    SAPROPHYTES.  83 

ena.  The  acid  salts  are  the  substances  which  are  most  actively  concerned 
in  reddening  the  blue  litmus  paper.  They  do  not  directly  aid  in  the  corro- 
sion phenomena.  In  the  soil,  however,  where  these  compounds  of  potash, 
phosphoric  acid,  etc.,  are  which  are  not  soluble  in  water,  the  acid  salt 
(primary  acid  potassium  phosphate)  which  is  most  actively  concerned  in 
reddening  the  blue  litmus  paper  may  act  indirectly  on  these  mineral  sub- 
stances, making  them  available  for  plant  food.  This  salt  soon  unites  with 
certain  chlorides  in  the  soil,  making  among  other  things  small  quantities 
of  hydrochloric  acid. 

176.  NOTE. — It  is  a  general  rule  that  plants  cannot  take  solid  food  into 
their  bodies,  but  obtain  all  food  in  either  a  liquid  or  gaseous  state.     The 
only  exception  to  this  is  in  the  case  of  the  plasmodia  of  certain  Myxomy- 
cetes  (Slime  Moulds),  and  also  perhaps  some  of  the  Flagellates  and  other 
very  low  forms,  which  engulf  solid  particles  of  food.     It  is  uncertain,  how- 
ever,   whether  these  organisms   belong  to  the  plant  or  animal  kingdom, 
and  they  probably  occupy  a  more  or  less  intermediate  position. 

177.  Action  of  nitrite  and  nitrate  bacteria. — Many  of  the  higher  green 
plants  prefer  their  nitrogenous  food  in  the  form  of  nitrates.     (Example, 
nitrate    of    soda,   potassium    nitrate,  saltpetre.)      Nitrates  are    constantly 

«ing  formed  in  soil  by  the  action  of  certain  bacteria.  The  nitrite  bacteria 
(Nitromonas)  convert  ammonia  in  the  soil  to  nitrous  acid  (a  nitrite),  while 
at  this  point  the  nitrate  bacteria  (Nitrobacter)  convert  the  nitrites  into 
nitrates.  The  fact  that  this  nitrification  is  going  on  constantly  in  soil  is  of 
the  utmost  importance,  for  while  commercial  nitrates  are  often  applied 
to  the  soil,  the  nitrates  are  easily  washed  from  the  soil  by  heavy  rains. 
These  nitrite  and  nitrate  bacteria  require  oxygen  for  their  activity,  and 
they  are  able  to  obtain  their  carbohydrates  by  decomposing  organic  matter 
in  the  soil,  or  directly  by  assimilating  the  CO2  in  the  soil,  deriving  the  energy 
for  the  assimilation  of  the  carbon  dioxide  from  the  chemical  process  of 
nitrification.  This  kind  of  carbon  dioxide  assimilation  is  called  chemo- 
synthetic  assimilation. 

2.   Parasites  and  Saprophytes. 

178.  Parasites    among   the   fungi. — A    parasite   is   an  organism  which 
derives  all  or  a  part  of  its  food  directly  from  another  living  organism  (its 
host)  and  at  the  latter's  expense.     The  larger  number  of  plant  parasites 
are  found  among  the  fungi  (rusts,  smuts,  mildews,  etc.).     (See  Nutrition  of 
the  Fungi,  paragraph  185.)     Some  of  these  are  not  capable  of  develop- 
ment unless  upon  their  host,  and  are  called  obligate  parasites.     Others  can 
grow  not  only  as  parasites  but  at  other  times  can  also  grow  on  dead  organic 
matter,  and  are   called  facultative  parasites,  i.e.  they  can  choose  either  a 
parasitic  life  or  a  saprophytic  one. 

179.  Parasites  among  the  seed  plants. — Cuscuta. — There  are,  however, 
parasites  among  the  seed  plants;  for  example,  the  dodder  (Cuscuta),  para- 


84 


PHYSIOLOGY. 


sitic  on  clover,  and  a  great  variety  of  other  plants.  There  is  food  enough 
in  the  seed  for  the  young  plant  to  take  root  and  develop  a  slender  stem  until 
it  takes  hold  of  its  host.  It  then  twines  around  the  stem  of  its  host  send- 
ing wedge-shaped  haustoria  into  the  stem  to  obtain  food.  The  part  then 
in  connection  with  the  ground  dies. 

The  haustoria  of  the  dodder  form  a  complete  junction  with  the  vascular 
bundles  of  its  host  so  that  through  the  vessels  water  and  salts  are  obtained, 
while  through  the  junction  of  sieve  tubes  the  elaborated  organic  food  is 


Fig.  74- 
Dcdder. 


obtained.  The  union  of  the  dodder  with  its  host  is  like  that  between  a 
graft  and  the  graft  stock.  The  beech  drops  (Epiphegus)  is  another  exam- 
ple of  a  parasitic  seed  plant.  It  is  parasitic  on  the  roots  of  the  beech. 

180.  The  mistletoe  (Phoradendron) ,  which  grows  on  the  branches  of 
trees,  sends  its  rootsinto  the  branches,  and  only  the  vessels  of  the  vascular 
system  are  fused  according  to  some.  If  this  is  true  then  it  probably  ob- 
tains only  water  and  salts  from  its  host.  But  the  mistletoe  has  green  leaves 
and  is  thus  able  to  assimilate  carbon  dioxide  and  manufacture  its  own 


AND    SAPROPHYTES.  85 

organic  substances.  It  is  claimed  by  some,  however,  that  the  host  derives 
some  food  from  the  parasite  during  the  winter  when  the  host  has  shed  its 
leaves,  and  if  this  is  true  it  would  seem  that  organic  food  could  also  be 
derived  during  the  summer  from  the  host  by  the  mistletoe. 

181.  Saprophytes. — A  saprophyte  is  a  plant  which  is  enabled  to  obtain 
its  food,  especially  its  organic;  food,  directly  from  dead  animals  or  plants  or 
from  dead  organic  substances.     Many  fungi  are  saprophytes,  as  the  moulds, 
mushrooms,  etc.     (See  Nutrition  of  the  Fungi.) 

182.  Humus  saprophytes. — The  action  of  fungi  as  described  in  the  pre- 
ceding chapter,  as  well  as  of  certain  bacteria,  gradually  converts  the  dead 
plants  or  plant  parts  into  the  finely  powdered  brown  substance  known  as 
humus.     In   general   the  green   plants   cannot  absorb  organic   food   from 
humus   directly.     But   plants   which   are   devoid   of   chlorophyll    can   live 
saprophytically  on  this  humus.     They  are  known  as  humus  saprophytes, 
Many  of  the  mushrooms  and  other  fungi,  as  well  as  some  seed  plants  which 
lack  chlorophyll  or  possess  only  a  small  quantity,  are  able  to  absorb  all 
their  organic  food  from  humus.     It  is  uncertain  whether  any  seed  plants 
can  obtain  all  of  their  organic  food  directly  from  humus,  though  it  is  be- 
lieved that  many  can  so  obtain  a  portion  of  it.     But  a  number  of  seed 
plants,  like  the  Indian  pipe  (Monotropa)  and  certain  orchids,  obtain  organic 
food  from  humus1.     These  plants  lack  chlorophyll  and  cannot  therefore 
manufacture  their  own  carbohydrate  food.     Not  being  parasitic  on  plants 
which  can,  as  in  the  case  of  the  dodder  and  beech  drops  mentioned  above, 
they  undoubtedly  derive  their  organic  food  from  the  humus.     But  fungus 
mycelium  growing  in  the  humus  is  attached  to  their,  roots,  and  in  some 
orchids  enters  the  roots  and  forms  a  nutritive  connection.     The  fungus 
mycelium  can  absorb  organic  food  from  the  humus  and  in  some  cases  at 
least  can  transfer  it  over  to  the  roots  of  the  higher  plant  (see  Mycorhiza). 

183.  Autotrophic,    heterotrophic,    and    mixotrophic  plants. — An    auto- 
trophic   plant  is  one  which  is  self-nourishing,  i.e.  it  is  provided  with  an 
abundant  chlorophyll  apparatus  for  carbon  dioxide  assimilation  and  with 
absorbing   organs   for   obtaining   water   and   salts.     Heterotrophic   plants 
are  not  provided  with  a  chlorophyll  apparatus  sufficient  to  assimilate  all 
the  carbon  dioxide  necessary,  so  they  nourish  themselves  by  other  means. 
Mixotrophic  plants  are  those  which  are  intermediate  between  the  other  two, 
i.e.  they  have  some  chlorophyll  but  not  enough  to  provide  all  the  organic 
food  necessary,  so  they  obtain  a  portion  of  it  by  other  means.     Evidently 
there  are  all  gradations  of  mixotrophic  plants  between  the  two  other  kinds 
(example,  the  mistletoe). 

184.  Symbiosis. — Symbiosis  means  a  living  with  or  living  together,  and 
is  said  of  those  organisms  which  live  so  closely  in  connection  with  each 
other  as  to  be  influenced  for  better  or  worse,  especially  from  a  nutrition 
standpoint.     Conjunctive   symbiosis   has   reference   to   those   cases   where 


86 


PHYSIO  LOG  Y. 


there  is  a  direct  interchange  of  food  material  between  the  two  organisms 
(lichens,  mycorhiza,  etc.)  Disjunctive  symbiosis  has  reference  to  an  inter 
life  relation  without  any  fixed  union  between  them  (example,  the  relations 
between  flowers  and  insects,  ants  and  plants,  and  even  in  a  broad  sense  the 
relation  between  saprophytic  plants  in  reducing  organic  matter  to  a  con- 
dition in  which  it  may  be  used  for  food  by  the  green  plants,  and  these  in 
turn  provide  organic  matter  for  the  saprophytes  to  feed  upon,  etc.).  Antag- 
onistic symbiosis  is  shown  in  the  relation  of  parasite  to  its  host,  reciprocal 
symbiosis,  or  mutualistic  symbiosis  is  shown  in  those  cases  where  both 
symbionts  derive  food  as  a  result  of  the  union  (lichens,  mycorhiza,  etc.). 

3.  How  Fungi  Obtain  their  Food. 

185.  Nutrition  of  moulds. — In  our  study  of  mucor,  as  we  have  seen,  the 

growing  or  vegetative  part 
of  the  plant,  the  mycelium, 
lies  within  the  substratum, 
which  contains  the  food 
materials  in  solution,  and  the 
slender  threads  are  thus 
bathed  on  all  sides  by  them. 
The  mycelium  absorbs  the 
watery  solutions  throughout 
the  entire  system  of  ramifica- 
tions. When  the  upright 
fruiting  threads  are  devel- 
oped they  derive  the  materials 
for  their  growth  directly  from 
the  mycelium  with  which 
they  are  in  connection.  The 
moulds  which  grow  on  de- 
caying fruit  or  on  other 
organic  matter  derive  their 
nutrient  materials  in  the  same 
way.  The  portion  of  the 
mould  which  we  usually  see 
on  the  surface  of  these  sub- 
stances is  in  general  the  fruit- 
ing part.  The  larger  part 
of  the  mycelium  lies  hidden 
within  the  subtratum. 
186.  Nutrition  of  para- 

Carnation  rust  on  leaf  and  flower  stem.    From  photo-  sitic  fungi.— Certain    of  the 
graph.  fungi  grow  on  or  within  the 

higher  plants  and  derive  their  food  materials  from  them  and  at  their  ex- 
pense. Such  a  fungus  is  called  a  parasite,  and  there  are  a  large  number 


HOW  PLANTS  OBTAIN  FOOD. 


of  these  plants  which  are  known  as  parasitic  fungi.     The  plant  at  whose 
expense  they  grow  is  called  the  "host." 

One  of  these  parasitic  fungi,  which  it  is  quite  easy  to  obtain  in  green- 
houses or  conservatories  during  the  autumn  and  winter,  is  the  carnation 
rust  (Uromyces  caryophyllinus},  since  it  breaks  out  in  rusty  dark  brown 
patches  on  the  leaves  and  stems  of  the  carnation  (see  fig.  75).  If  we  make 
thin  cross  sections  through  one  of  these  spots  on  a  leaf,  and  place  them  for  a 


Fig.  76. 
Several  teleutospores,  showing  the  variations  in  form. 

few  minutes  in  a  solution  of  chloral  hydrate,  portions  of  the  tissues  of  the 
leaf  will  be  dissolved.  After  a  few  minutes  we  wash  the  sections  in  water  on 
a  glass  slip,  and  stain  them  with  a  solution  of  eosin.  If  the  sections  were  care- 


Fig.  77. 

Cells  from  the  stem  of  a  rusted  carnation,  showing  the  intercellular  mycelium  and  haustoria. 
Object  magnified  30  times  more  than  the  scale. 

fully  made,  and  thin,  the  threads  of  the  mycelium  will  be  seen  coursing  be- 
tween the  cells  of  the  leaf  as  slender  threads.  Here  and  there  will  be  seen 
short  branches  of  these  threads  which  penetrate  the  cell  wall  of  the  host  and 
project  into  the  interior  of  the  cell  in  the  form  of  an  irregular  knob.  Such 
a  branch  is  a  haustorium.  By  means  of  this  haustorium,  which  is  here 


88 


PHYSIOLOGY. 


only  a  short  branch  of  the  mycelium,  nutritive  substances  are  taken  by  the 
fungus  from  the  protoplasm  or  cell-sap  of  the  carnation.  From  here  it 
passes  to  the  threads  of  the  mycelium.  These  in  turn  supply  food  material 
for  the  development  of  the  dark  brown  gonidia,  which  we  see  form  the  dark- 
looking  powder  on  the  spots.  Many  other  fungi  form  haustoria,  which  take 
up  nutrient  matters  in  the  way  described  for  the  carnation  rust.  In  the  case 


\f 


Fig.  78. 


Fig.  79- 


^ 

Cell  from  carnation   leaf,   showing  Intercellular   mycelium  with    haustoria   entering 

haustoriuin  of  rust  mycelium  grasping       the  cells.     A ,  of  Cystopus  candidus  (white   rust) ; 
the  nucleus  of  the  host.      '     ' 
um  ;  n,  nucleus  of  host. 


me  ecus,      ^i ,  01   ^ysiopus  caiiuiuus    iwmi 
B,  of  Peronospora  calotheca.     (De  Bary.) 


of  other  parasitic  fungi  the  threads  of  the  mycelium  themselves  penetrate 
the  cells  of  the  host,  while  in  still  others  the  mycelium  courses  only  between 
the  cells  of  the  host  (fungus  of  peach  leaf-curl  for  example)  and  derives  food 
materials  from  the  protoplasm  or  cell-sap  of  the  host  by  the  process  of 


187.  Nutrition  of  the  larger  fungi. — If  we  select  some  one 
of  the  larger  fungi,  the  majority  of  which  belong  to  the  mush- 
room family  and  its  relatives,  which  is  growing  on  a  decaying  log 
or  in  the  soil,  we  shall  see  on  tearing  open  the  log,  or  on  remov- 
ing the  bark  or  part  of  the  soil,  as  the  case  may  be,  that  the 
stem  of  the  plant,  if  it  have  one,  is  connected  with  whitish 
strands.  During  the  spring,  summer,  or  autumn  months,  exam- 
ples of  the  mushrooms  connected  with  these  strands  may  usually 
be  found  readily  in  the  fields  or  woods,  but  during  the  winter  and 


HOW  PLANTS  OBTAIN  FOOD. 


89 


colder  parts  of  the  year  often  they  may  be  seen  in  forcing  houses, 
especially  those  cellars  devoted  to  the  propagation  of  the  mush- 
room of  commerce. 

188.  These  strands  are  made  up  of  numerous  threads  of  the 
mycelium  which  are  closely  twisted  and  interwoven  into  a  cord 
or  strand,  which  is    called  a  mycelium   strand,  or  rhizomorph. 
These  are  well  shown  in  fig.    236,  which  is  from  a  photograph  of 
the  mycelium  strands,  or  ' '  spawn  ' '  as  the  grower  of  mushrooms 
calls  it,  of  Agaricus  campestris.    The  little  knobs  or  enlargements 
on  the  strands  are  the  young  fruit  bodies,  or  ' '  buttons. ' ' 

189.  While  these  threads  or  strands  of  the  mycelium  in  the 
decaying  wood  or  in  the  decaying  organic  matter  of  the  soil  are 


Fig.  80. 


Sterile  mycelium  on  wood  props  in  coal  mine,  400  feet  below  surface.     (Photographed  by 
the  author.) 


QO  PHYSIOLOGY. 

not  true  roots,  they  function  as  roots,  or  root  hairs,  in  the  ab- 
sorption of  food  materials.  In  old  cellars  and  on  damp  soil  in 
moist  places  we  sometimes  see  fine  examples  of  this  vegetative 
part  of  the  fungi,  the  mycelium.  But  most  magnificent  examples 
are  to  be  seen  in  abandoned  mines  where  timber  has  been  taken 
down  into  the  tunnels  far  below  the  surface  of  the  ground  to 
support  the  rock  roof  above  the  mining  operations.  I  have 
visited  some  of  the  coal  mines  at  Wilkesbarre,  Pa. ,  and  here  on 
the  wood  props  and  doors,  several  hundred  feet  below  the  surface, 
and  in  blackest  darkness,  in  an  atmosphere  almost  completely 
saturated  at  all  times,  the  mycelium  of  some  of  the  wood-destroy- 
ing fungi  grows  in  a  profusion  and  magnificence  which  is  almost 
beyond  belief.  Fig.  80  is  from  a  flash-light  photograph  of  a 
beautiful  example  400  feet  below  the  surface  of  the  ground. 
This  was  growing  over  the  surface  of  a  wood  prop  or  post,  and 
the  picture  is  much  reduced.  On  the  doors  in  the  mine  one  can 
see  the  strands  of  the  mycelium  which  radiate  in  fan-like  figures 
at  certain  places  near  the  margin  of  growth,  and  farther  back  the 
delicate  tassels  of  mycelium  which  hang  down  in  fantastic  figures, 
all  in  spotless  white  and  rivalling  the  most  beautiful  fabric  in  the 
exquisiteness  of  its  construction. 

190.  How  fungi  derive  carbohydrate  food. — The  fungi  being  devoid  of 
chlorophyll  cannot  assimilate  the  CO2  from  the  air.  They  are  therefore 
dependent  on  the  green  plants  for  their  carbohydrate  food.  Among  the 
saprophytes,*  the  leaf  and  wood  destroying  fungi  excrete  certain  substances 
(known  as  enzymes)  which  dissolve  the  carbohydrates  and  certain  other 
organic  compounds  in  the  woody  or  leafy  substratum  in  which  they  grow. 
They  thus  produce  a  sort  of  extracellular  digestion  of  carbohydrates,  con- 
verting them  into  a  soluble  form  which  can  be  absorbed  by  the  mycelium. 
The  parasitic  fungi  also  obtain  their  carbohydrates  and  other  organic  food 
from  the  host.  The  mycelium  of  certain  parasitic,  and  of  wood  destroying 
fungi,  excretes  enzymes  (cytase)  which  dissolve  minute  perforations  in  the 
cell  walls  of  the  host  and  thus  aid  the  hypha  during  its  boring  action  in 
penetrating  cell  walls. 

NOTE. — Certain  wood  destroying  fungi  growing  in  oaks  absorb  tannin 
directly,  i.e.  in  an  unchanged  form.  One  of  the  pine  destroying  fungi 
(Trametes  pint)  absorbs  the  xylogen  from  the  wood  cells,  leaving  the  pure 
cellulose  in  which  the  xylogen  was  nitrated;  while  Polyporus  mollis  absorbs 
the  cellulose,  leaving  behind  only  the  wood  element. 


HOW  PLANTS   OBTAIN  FOOD.  9 1 

4.  Mycorhiza. 

191.  While  such  plants  as  the  Indian  pipe  (Monotropa),  some  of  the 
orchids,  etc.,  are  humus  saprophytes  and  some  of  them  are  possibly  able  to 
absorb  organic  food  from  the  humus,  many  of  them  have  fungus  mycelium 
in  close  connection  with  their  roots,  and  these  fungus  threads  aid  in  the 
absorption  of  organic  food.     The  roots  of  plants  which  have  fungus  myce- 
lium intimately  associated  in  connection  with  the  process  of  nutrition,  are 
termed  mycorhiza.     There  is  a  mutual  interchange  of  food  between  the 
fungus  and  the  host,  a  reciprocal  symbiosis. 

192.  Mycorhiza  are  of  two  kinds  as  regards  the  relation  of  the  fungus  to 
the  root;    ectotrophic  (or  epiphytic),  where  the  mycelium  is  chiefly  on  the 
outside  of  the  root,  and  endotrophic  (or  enaophytic]  where  the  mycelium  is 
chiefly  within  the  tissue  of  the  root. 

193.  Ectotrophic  mycorhiza. — Ectotrophic  mycorhiza  occur  on  the  roots 
of  the  oak,  beech,  hornbean,  etc.,  in  forests  where  there  is  a  great  deal  of 
humus  from  decaying  leaves  and  other  vegetation.     The  young  growing 
roots  of  these  trees  become  closely  covered  with  a  thick  felt  of  the  mycelium, 
so  that  no  root  hairs  can  develop.     The  terminal  roots  also  branch  pro- 
fusely and  are  considerably  thickened.     The   fungus  serves  here  as  the 
absorbent  organ  for  the  tree.     It  also  acts  on  the  humus,  converting  some 
of  it  into  available  plant  food  and  transferring  it  over  to  the  tree. 

194.  Endotrophic  mycorhiza. — These  are  found  on  many  of  the  humus 
saprophytes,  which  are  devoid  of  chlorophyll,  as  well  as  on  those  possess- 
ing little  or  even  on  some  plants  possessing  an  abundance,  of  chlorophyll. 
Examples  are  found  in  many  orchids  (see  the  coral  root  orchid,  for  exam- 
ple), some  of  the  ferns  (Botrychium),  the  pines,  leguminous  plants,  etc. 
In  endotrophic  mycorhiza  the  mycelium  is  more  abundant  within  the  tissues 
of  the  root,  though  some  of  the  threads  extend  to  the  outside.     In  the  case 
of  the  mycorhiza  on  the  humus  saprophytes  which  have  no  chlorophyll,  or 
but  little,  it  is  thought  by  some  that  the  fungus  mycelium  in  the  humus 
assists  in  converting  organic  substances  and   carbohydrates  into  a  form 
available  for  food  by  the  higher  plant  and  then  conducts  it  into  the  root, 
thus  aiding  also  in  the  process  of  absorption,  since  there  are  few  or  no  root 
hairs  on  the  short  and  fleshy  mycorhiza.     The  roots,  however,  of  some  of 
these  humus  saprophytes  have  the  power  of  absorbing  a  portion  of  their 
organic  compounds  from  the  humus.     It  is  thought  by  some,  though  not 
definitely  demonstrated,  that  in  the  case  of  the  oaks,  beeches,  hornbeans, 
and  other  chlorophyll-bearing  symbionts,  the  fungus  threads  do  not  absorb 
any  carbohydrates  for  the  higher  symbiont,  but  that  they  actually  derive 
their  carbohydrates  from  it.*     But  it  is  reasonably  certain  that  the  fungus 

*  Lvidence  points  to  the  belief  that  certain  cells  of  the  host  form  substances 
which  iitiract,  chemitropically,  the  fungus  threads,  and  that  in  these  cells  the 
iungus  threads  are  more  abundant  than  in  others.  Furthermore  in  the  vi- 
cinity of  the  nucleus  of  the  host  seems  to  be  the  place  where  these  activities 
are  more  marked. 


92 


PHYSIOLOGY. 


threads  do  assimilate  from  the  humus  certain  unoxidized,  or  feebly  oxi- 
dized, nitrogenous  substances  (ammonia,  for  example),  and  transfer  them 
over  to  the  host,  for  the  higher  plants  with  difficulty  absorb  these  sub- 
stances, while  they  readily  absorb  nitrates  which  are  not  abundant  in 
humus.  This  is  especially  important  in  the  forest.  It  is  likely  therefore 
that  the  fungus  symbiont  supplies  nitrogen  to  its  host,  though  it  does  not 
assimilate  free  nitrogen  as  is  the  case  in  the  following  examples. 

5.  Nitrogen  gatherers. 

195.  How  clovers,  peas,  and  other  legumes  gather  nitrogen. — It  has  long 
been  known  that  clover  plants,  peas,  beans,  and 
many  other  leguminous  plants  are  often  able  to 
thrive  in  soil  where  the  cereals  do  but  poorly. 
Soil  poor  in  nitrogenous  plant  food  becomes  richer 
in  this  substance  where  clovers,  peas,  etc.,  are 
grown,  and  they  are  often  planted  for  the  purpose 
of  enriching  the  soil.  Leguminous  plants,  espe- 
cially in  poor  soil,  are  almost  certain  to  have  en- 
largements, in  the  form  of  nodules,  or  "root 
tubercles."  A  root  of  the  common  vetch  with 
some  of  these  root  tubercles  is  shown  in  fig.  81. 

196.  A  fungal  or  bacterial  organism  in  these 
root  tubercles. — If  we  cut  one  of  these  root  tuber- 
cles open,  and  mount  a  small  portion  of  the  in- 
terior in  water  for  examination  with  the  micro- 
scope, we  shall  find  small  rod-shaped  bodies, 
some  of  which  resemble  bacteria,  while  others  are  more  or  less  forked  into 
forms  like  the  letter  Y,  as  shown  in  fig.  82.  These  bodies  are  rich  in 
nitrogenous  substances,  or  proteids.  They  are  portions  of  a  minute  organism, 
of  a  fungus  or  bacterial  nature,  which  attacks  the  roots  of  leguminous  plants 


Fig.  81. 

Root  of  the  common  vetch, 
showing  root  tubercles. 


Fig.  82.  Fig.  83. 

Root-tubercle  organism  from  vetch,  old  con-        Root-tubercle  organism  from   Medicago 
dition.  denticulata. 

and  causes  these  nodular  outgrowths.     The  organism  (Phytomyxa  legumi- 
nosarum)  exists  in  the  soil  and  is  widely  distributed  where  legumes  grow. 


HOW  PLANTS   OBTAIN  FOOD.  93 

197.  How  the  organism  gets  into  the  roots  of  the  legumes. — This  minute 
organism  in  the  soil  makes  its  way  through  the  wall  of  a  root  hair  near  the 
end.     It  then  grows  down  the  interior  of  the  root  hair  in  the  form  of  a 
thread.     When    it   reaches   the  cell  walls  it  makes  a  minute  perforation, 
through  which  it  grows  to  enter  the  adjacent  cell,  when  it  enlarges  again. 
In  this  way  it  passes  from  the  root  hair  to  the  cells  of  the  root  and  down  to 
near  the  center  of  the  root.     As  soon  as  it  begins  to  enter  the  cells  of  the 
root  it  stimulates  the  cells  of  that  portion  to  greater  activity.     So  the  root 
here  develops   a   large   lateral  nodule,  or   "root  tubercle."     As  this  "root 
tubercle"  increases  in  size,   the  fungus  threads  branch  in  all  directions, 
entering  many  cells.      The  threads  are  very  irregular  in  form,  and  from  cer- 
tain enlargements   it  appears  that  the  rod-like  bodies  are  formed,   or   the 
thread  later  breaks  into  myriads  of  these  small  "  bacteroids. " 

198.  The   root  organism  assimilates  free  nitrogen  for  its  host. — This 
organism  assimilates  the  free  nitrogen  from  the  air  in  the  soil,  to  make  the 
proteid  substance  which  is  found  stored  in  the  bacteroids^in  large  quantities. 
Some  of  the  bacteroids,  rich  in  proteids,  are  dissolved,  and  the  proteid  sub- 
stance is  made  use  of  by  the  clover  or  pea,  as  the  case  may  be.  This  is  why 
such  plants  can  thrive  in  soil  with  a  poor  nitrogen  content.     Later  in  the 
season  some  of  the  root  .tubercles  die  and  decay.     In  this  way  some  of  the 
proteid  substance  is  set  free  in  the  soil.    JThe  soil  thus  becomes  richer  in 
nitrogenous  plant  food. 

The  forms  of  the  bacteroids  vary.  In  some  of  the  clovers  they  are  oval, 
in  vetch  they  are  rod-like  or  forked,  and  other  forms  occur  in  some  of  the 
other  genera. 

199.  NOTE. — So  far  as  we  know  the  legume  tubercle  organism  does  not 
assimilate  free  nitrogen  of  the  air  unless  it  is  within  the  root  of  the  legume. 
But  there  are  microorganisms  in  the  soil  which  are  capable  of  assimilating 
free  nitrogen  independently.     Example,  a  bacterium,  Clortridium  pasteur- 
ianum.     Certain  bacteria  and  algae  live  in  contact  symbiosis  in  the  soil,  the 
bacteria  fixing  free  nitrogen,  while  in  return  for  the  combined  nitrogen,  the 
algae  furnish  the  bacteria  with  carbohydrates.     It  seems  that  these  bac- 
teria cannot  fix  the  free  nitrogen  of  the  air  unless  they  are  supplied  with 
carbohydrates,  and  it  is  known  that  Clostridium  pasteurianum  cannot  assim- 
ilate free  nitrogen  unless  sugar  is  present. 

6.  Lichens. 


200.  Nutrition  of  lichens. — Lichens  are  very  curious  plants  which  grow 
on  rocks,  on  the  trunks  and  branches  of  trees,  and  on  the  soil.  They  form 
leaf-like  expansions  more  or  less  green  in  color,  or  brownish,  or  gray,  or  they 
occur  in  the  form  of  threads,  or  small  tree-like  formations.  Sometimes  the 


94 


PHYSIOLOG  Y. 


plant  fits  so  closely  to  the  rock  on  which  it  grows  that  it  seems  merely  U. 
paint  the  rock  a  slightly  different  color,  and  in  the  case  of  many  which  occur  on 
trees  there  appears  to  be  to  the  eye  only  a  very  slight  discoloration  of  the  bark 
of  the  trunk,  with  here  and  there  the  darker  colored  points  where  fruit  bodies 


Fig.  84. 
Frond  of  lichen  (peltigera),  showing  rhizoids. 

are  formed.  The  most  curious  thing  about  them  is,  however,  that  while  they 
form  plant  bodies  of  various  form,  these  bodies  are  of  a  "dual  nature"  as 
regards  the  organisms  composing  them.  The  plant  bodies,  in  other  words,  are 
formed  of  two  different  organisms  which,  woven  together,  exist  apparently 
as  one.  A  fungus  on  the  one  hand  grows  around  and  encloses  in  the 
meshes  of  its  mycelium  the  cells  or  threads  of  an  alga,  as  the  case  may  be. 

If  we  take  one  of  the  leaf-like  forms  known  as  peltigera,  which  grows  on 
damp  soil  or  on  the  surfaces  of  badly  decayed  logs,  we  see  that  the  plant 
body  is  flattened,  thin,  crumpled,  and  irregularly  lobed.  The  color  is  dull 
greenish  on  the  upper  side,  while  the  under  'side  is  white  or  light  gray,  and 
mottled  with  brown,  especially  the  older  portions.  Here  and  there  on  the 
under  surface  are  quite  long  slender  blackish  strands.  These  are  composed 
entirely  of  fungus  threads,  and  serve  as  organs  of  attachment  or  holdfasts, 
and  for  the  purpose  of  supplying  the  plant  body  with  mineral  substances 
which  are  in  solution  in  the  water  of  the  soil.  If  we  make  a  thin  section  of 
the  leaf-like  portion  of  a  lichen  as  shown  in  fig.  85,  we  shall  see  that  it  is 
composed  of  a  mesh  of  colorless  threads  which  in  certain  definite  portions 
contain  entangled  green  cells.  The  colorless  threads  are  those  of  the  fungus, 
while  the  green  cells  are  those  of  the  alga.  These  green  cells  of  the  alga  per- 
form the  function  of  chlorophyll  bodies  for  the  dual  organism,  while  the  threads 
of  the  fungus  provide  the  mineral  constituents  of  plant  food.  The  alga, 


HOW  PLANTS   OBTAIN  FOOD. 


95 


while  it  is  not  killed  in  the  embrace  of  the  fungus,  does  not  reach  the  per- 
fect state  of  development  which  it  attains  when  not  in  connection  with  the 
fungus.  On  the  other  hand  the  fungus  profits  more  than  the  alga  by  this 
association.  It  forms  fruit  bodies,  and  perfects  spores  in  the  special  fruit 
bodies,  which  are  so  very  distinct  in  the  case  of  so  many  of  the  species  of 
the  lichens.  These  plants  have  lived  for  so  long  a  time  in  this  close  associa- 
tion that  the  fungi  are  rarely  found  separate  from  the  algae  in  nature,  but  in 
a  number  of  cases  they  have  been  induced  to  grow  in  artificial  cultures  sep- 


Fig.  85. 

Lichen  (peltigera),  section  of  thallus  ;  dark  zone  of  rounded  bodies  made  up  largely  of  the 
algal  cells.     Fungus  cells  above,  and  threads  beneath  and  among  the  algal  cells. 


irate  from  the  alga.  This  fact,  and  also  the  fact  that  the  algae  are  often 
found  to  occur  separate  from  the  fungus  in  nature,  is  regarded  by  many  as  an 
indication  that  the  plant  body  of  the  lichens  is  composed  of  two  distinct  or- 
ganisms, and  that  the  fungus  is  parasitic  on  the  alga. 

201.  Others  regard  the  lichens  as  autonomous  plants,  that  is,  the  two  or- 
ganisms have  by  this  long-continued  community  of  existence  become  unified 
into  an  individualized  organism,  which  possesses  a  habit  and  mode  of  life 


PHYSIOLOGY. 


distinct  from  that  of  either  of  the  organisms  forming  the  component  parts. 
This  community  of  existence  between  two  different  organisms  is  called  by 
some  mutualism,  or  symbiosis.  While  the  alga  inclosed  within  the  meshes 
of  the  fungus  is  not  so  free  to  develop,  and  probably  does  not  attain  the  full 
development  which  it  would  alone  under  favorable  conditions,  still  it  is 


Fig.  86. 

Section  of  fruit  body  or  apothecium  of  lichen  (parmelia),  showing  asci  and  spores 
of  the  fungus. 

very  likely  that  it  is  often  preserved  from   destruction   during  very  dry 
periods,  within  the  tough  thallus,  on  the  surface  of  bare  rocks. 


CHAPTER    X. 

HOW   PLANTS   OBTAIN   THEIR   FOOD,    II. 
Seedlings. 

202.  It  is  evident  from  some  of  the  studies  which  we  have  made  in  con- 
nection with  germination  of  seeds  and  nutrition  of  the  plant  that  there  is  a 
period  in  the  life  of  the  seed  plants  in  which  they  are  able  to  grow  if  sup- 
plied with  moisture,  but  may  entirely  lack  any  supply  of  food  substance 
from  the  outside,  though  we  understand  that  growth  finally  comes  to  a 
standstill  unless  they  are  supplied  with  food  from  the  outside.     In  con- 
nection with  the  study  of  the  nutrition  of  the  plant,  therefore,  it  will  be  well 
to  study  some  of  the  representative  seeds  and  seedlings  to  learn  more  accu- 
rately the  method  of  germination  and  nutrition  in  seedlings  during  the  ger- 
minating period. 

203.  To  prepare  seeds   for   germination. — Soak  a  handful  of  seeds  (or 
more  if  the  class  is  large)  in  water  for  12  to  24  hours.     Take  shallow  crockery 
plates,  or  ordinary  plates,  or  a  germinator  with  a  fluted  bottom.     Place  in 
the  bottom  some  sheets  of  paper,  and  if  sphagnum  moss  is  at  hand  scatter 
some  over  the  paper.     If  the  moss  is  not  at  hand,  throw  the  upper  layer  of 
paper  into  numerous  folds.     Thoroughly  wet  the  paper  and  moss,  but  do 
not  have  an  excess  of  water.     Scatter  the  seeds  among  the  moss  or  the  folds 
of  the  paper.     Cover  with  some  more  wet  paper  and  keep  in  a  room  where 
the  temperature  is  about  20°  C.  to  25°  C.     The  germinator  should  be  looked 
after  to  see  that  the  paper  does  not  become  dry.     It  may  be  necessary  to 
cover  it  with  another  vessel  to  prevent  the  too  rapid  evaporation  of  the  water. 
The  germinator  should  be  started  about  a  week  before  the  seedlings  are 
wanted  for  study.      Some  of  the  soaked  seeds  should  be  planted  in  soil  in 
pots  and  kept  at  the  same  temperature,  for  comparison  with  those  grown  in 
the  germinator. 

204.  Structure  of  the  grain  of  corn. — Take  grains  of  corn  that  have  been 

97 


9^  PHYSIOLOG  Y. 

soaked  in  water  for  24  hours  and  note  the  form  and  difference  in  the  two 
sides  (in  all  of  these  studies  the  form  and  structure  of  the  seed,  as  well  as 
the  stages  in  germination,  should  be  illustrated  by  the  student).  Make  a 
longisection  of  a  grain  of  corn  through  the  middle  line,  if  necessary 
making  several  in  order  to  obtain  one  which  shows  the  structures  well  near 
the  smaller  end  of  the  grain.  Note  the  following  structures:  ist,  the  hard 

outer  "wall"  (formed  of  the  consoli- 
dated wall  of  the  ovary  with  the  in- 
teguments of  the  ovules — see  Chap- 
ters  35  and  36);  ad,  the  greater  mass 

Section  of  com  sSdf'at  upper  right  of  of  starch  and  other  Plant  food  (the 
each  is  the  plantlet,  next  the  cotyledon,  at  endosperm)  in  the  centre:  ?d,  a  some- 
left  the  endosperm.  '  °  ' 

what    crescent-shaped     body      (the 

scutellum)  lying  next  the  endosperm  and  near  the  smaller  end  of  the 
grain;  4th,  the  remaining  portion  of  the  young  embryo  lying  between  the 
scutellum  and  the  seed  coat  in  the  depression.  When  good  sections  are 
made  one  can  make  out  the  radicle  at  the  smaller  end  of  the  seed,  and  a 
few  successive  leaves  (the  plumule)  which  lie  at  the  opposite  end  of  the 
embryo  shown  by  sharply  cuived  parallel  lines.  Observe  the  attachment 
of  the  scutellum  to  the  caulicle  at  the  point  of  junction  of  the  plumule  and 
the  radicle.  The  scutellum  is  a  part  of  the  embryo  and  represents  a  coty- 
ledon. The  endosperm  is  also  called  albumen,  and  such  a  seed  is  albumin- 
ous. \  "+ 

Dissect  out  an  embryo  from  another  seed,  and  compare  with  that  seen  in 
the  section. 

205.  In  the  germination  of  the  grain  of  corn  the  endosperm  supplies  the 
food  for  the  growth  of  the  embryo  until  the  roots  are  well  established  in 
the  soil  and  the  leaves  have  become  expanded  and  green,  in  which  stage 
the  plant  has  become  able  to  obtain  its  food  from  the  soil  and  air  and  live 
independently.  The  starch  in  the  endosperm  cannot  of  course  be  used  for 
food  by  the  embryo  in  the  form  of  starch.  It  is  first  converted  into  a  solu- 
ble form  and  then  absorbed  through  the  surface  of  the  scutellum  or  coty- 
ledon and  carried  to  all  parts  of  the  embryo.  An  enzyme  developed  by  the 
embryo  acts  upon  the  starch,  converting  it  into  a  form  of  sugar  which  is  in 
solution  and  can  thus  be  absorbed.  This  enzyme  is  one  of  the  so-called 
diastatic  "  ferments  "  which  are  formed  during  the  germination  of  all  seeds 
which  contain  food  stored  in  the  form  of  starch.  In  some  seedlings, 
this  diastase  formed  is  developed  in  much  greater  abundance  than  in 
others,  for  example,  in  barley.  Examine  grains  of  corn  still  attached 
to  seedlings  several  weeks  old  and  note  that  a  large  part  of  their  content 
has  been  used  up.  The  action  of  diastase  on  starch  is  described  in 
Chapter  8. 


HOW  PLANTS   OBTAIN    THE  IF  FOOD.  99 

206.  Structure  of  the  pumpkin  seed. — The  pumpkin  seed  has 
a  tough  papery  outer  covering  for  the  protection  of  the  embryo 
plant   within.      This   covering   is   made  up   of  the   seed  coats. 
When  the  seed  is  opened  by  slitting  off  these  coats  there  is  seen 
within   the  "meat"   of  the   pumpkin    seed.      This  is  nothing 
more  than  the  embryo  plant.      The  larger  part  of  this  embryo 
consists  of  two  flattened  bodies  which  are  more  prominent  than 
any  other  part  of  the  plantlet  at  this  time.      These  two  flattened 
bodies  are  the  two  first  leaves,  usually  called  cotyledons.      If  we 
spread  these  cotyledons  apart  we  see  that  they  are  connected  at 
one  end.      Lying  between  them  at  this  point  of  attachment  is  a 
small  bud.      This  is  the  plumule.      The  plumule  consists  of  the 
very  young  leaves  at  the  end  of  the  stem  which  will  grow  as  the 
seed  germinates.      At  the  other  end  where  the  cotyledons  are 
joined  is  a  small  projection,  the  young  root,  often  termed  the 
radicle. 

207.  How  the  embryo  gets  out  of  a  pumpkin  seed. — To  see 
how    the    embryo    gets   out   of  the   pumpkin   seed   we   should 
examine  seeds  germinated  in  the  folds  of  damp  paper  or  on  damp 
sphagnum,  as  well  as  some  which  have  been  germinated*  in  earth. 
Seeds  should  be  selected  which  represent  several  different  stages 
of  germination. 


Fig.  88. 

Germinating  seed  of  pumpkin,  showing  how  the  heel  or  "  peg  "  catches  on  the  seed  coat 
to  cast  it  off. 

208.  The  peg  helps  to  pull  the  seed  coats  apart. — The  root 
pushes  its  way  out  from  between  the  stout  seed  coats  at  the 
smaller  end,  and  then  turns  downward  unless  prevented  from  so 


100 


PHYSIOLOGY. 


doing  by  a  hard  surface.      After  the  root  is  2-^cm  long,  and  the 
two  halves  of  the  seed  coats  have  begun  to  be  pried  apart,  if  we 

look  in  this  rift  at  the 
junction    of    the    root 
and  stem,  we  shall  see 
that  one  end  of  the  seed 
coat  is  caught  against 
a    heel,     or     "peg," 
which    has    grownt  out 
from  the  stem  for  this 
purpose.      Now    if   we 
examine  one  which  is 
a  little 
more  ad- 
vanced, 


Fig.  89. 
Escape  of  the  pumpkin  seedling  from  the  seed  coats. 


we  shall  see  this  heel 
more  distinctly,  and 
also  that  the  stem  is 
arching  out  away  from 
the  seed  coats.  As  the 
stem  arches  up  its  back 
in  this  way  it  pries  wjth 
the  cotyledons  against 
the  upper  seed  coat, 
but  the  lower  seed  coat 
is  caught  against  this  heel,  and  the  two  are  pulled  gradually 
apart.  In  this  way  the  embryo  plant  pulls  itself  out  from  be- 
tween the  seed  coats.  In  the  case  of  seeds  which  are  planted 
deeply  in  the  soil  we  do  not  see  this  contrivance  unless  we  dig 
down  into  the  earth.  The  stem  of  the  seedling  arches  through 
the  soil,  pulling  the  cotyledons  up  at  one  end.  Then  it 
straightens  up,  the  green  cotyledons  part,  and  open  out  their 
inner  faces  to  the  sunlight,  as  shown  in  fig.  90.  If  we  dig  into 
the  soil  we  shall  see  that  this  same  heel  is  formed  on  the  stem, 
and  that  the  seed  coats  are  cast  off  into  the  soil. 


HO W  PLANTS   OBTAIN   THKlR   POOb.  10 1 


209.  Parts  of  the  pumpkin  seedling. — During  the  germination 
of  the  seed  all   parts  of  the  embryo  have  enlarged.      This  in- 
crease in  size  of  a  plant  is  one  of  the  peculiarities  of  growth. 
The  cotyledons  have  elongated  and  expanded  somewhat,  though 
not    to   such  a   great  extent  as  the  root  and   the   stem.      The 
cotyledons  also  have  become  green  on  exposure  to  the  light. 
Very  soon  after  the  main  root  has  emerged  from  the  seed  coats, 
other  lateral  roots  begin  to  form,  so  that  the 

root  soon  becomes  very  much  branched. 
The  main   root  with  its  branches  makes 
up   the  root  system  of  the  seedling.      Be- 
tween the    expanded    cotyledons  is    seen 
the   plumule.      This  has   enlarged    some- 
what, but  not  nearly  so  much  as  the  root, 
or  the  part    of   the  stem    which    extends 
below  the  cotyledons.      This  part  of  the 
stem,    i.e.,    that 
part     below    the 
cotyledons     and 
extending  to  the 
beginning  of  the 
root,  is  called  in  Fig.  go. 

...  Pumpkin  seedling  rising  from  the  ground* 

all  seedlings  the 

hypocolyl,  which  means  "  below  the  cotyledon." 

210.  The  common  garden  bean. — The  common  garden  bean 
or  the  lima  bean,  may  be  used  for  study.     The  garden  bean  is 
not  so  flattened  or  broadened  as  the  lima  bean.     It  is  rounded- 
compressed,  elongate  slightly  curved,   slightly  concave  on  one 
side  and  convex  on  the  other,  and  the  end*  are  rounded.     At 
the  middle  of  the  concave  side  note  the  distinct  scar  (the  hilum) 
formed  where  the  bean  seed  separates  from  its  attachment  to 
the  wall  of  the  pod.     Upon  one  side  of  this  scar  is  a  slight  prom- 
inence which  is  continued  for  a  short  distance  toward  the  end 
of  the  bean  in  the  form  of  a  slight  ridge.     This  is  the  raphe,  and 
represents  that  part  of  the  stalk  of  the  ovule  which  is  joined  to 
the  side  of  the  ovule  when  the  latter  is  curved  around  against  it 


IO2 


PHYSIOLOG  Y. 


(see  Chapter  36)7  and1  at  the  outer  end  of  the  raphe  is  the  cha- 
laza,  the  point  where  the  stalk  is  joined  to  the  end  of  the  ovule, 
best   understood  in  a  straight  ovule       Upon   the 
opposite   side  of  the    scar  and  close  to  it  can  be 
m  seen  a  minute  depression,  the  micropyle.      Under- 
neath  the  seed  coat   and  lying  between  this  point 
and  the  end  of  the  seed  is  the  embryo,  which  gives 
greater  prominence  to  the  bean  at  this  point,  but  it 
is  especially  more  prominent  after  the  bean  has  been 
soaked  in  water.     Soak  the  beans  in  water  and  as 
Garden  bean,  they  are  swelling  note  how  the  seed  coats  swell 


!  faster  than  the  inner  portion  of  the  seed,  which 
causes  them  to  wrinkle  in  a  curious  way,  but  finally 
the  inner  portion  swells  and  fills  the  seed  coat  out 

smooth  again.     Sketch  a  bean  showing  all  the  external  features 

both  in  side  view  and  in  front.     Split  one  lengthwise  and  sketch 

the  half  to  which   the   embryo   clings,  noting    the  young   root, 

stem,  and  the  small   leaves  which  were  lying 

between   the    cotyledons.     There   is  no   endo- 

sperm here  now,  since  it  was  all  used  up  in 

the  growth  of  the  embryo,  and  a  large  part  of 

its  substance  was  stored  up  in  the  cotyledons. 

As  the  seed  germinates  the  young  plant  gets  its 

first  food  from  that  stored  in  the  cotyledons. 

J 

The  hypocotyl  elongates,  becomes  strongly  let- 
arched,  and  at  last  straightens  up,  lifting  the  cotyledons  from 
th*j  soil.  As  the  cotyledons  become  exposed  to  the  light  they 
assume  a  green  color.  Some  of  the  stored  food  in  them  goes 
to  nourish  the  embryo  during  germination,  and  they  therefore 
become  smaller,  shrivel  somewhat,  and  at  last  fall  off. 

211.  The  castor-  oil  bean.  —  This  is  not  a  true  bean,  since  it 
belongs  to  a  very  different  family  of  plants  (Euphorbiaceae).  In 
the  germination  of  this  seed  a  very  interesting  comparison  can 
be  mad?  with  that  of  the  garden  bean.  As  the  "bean"  swells 
the  very  hard  outer  coat  generally  breaks  open  at  the  free  end 
and  slips  off  at  the  stem  end.  The  next  coat  within,  which  is 


pjg>  Q2> 
Bean   teed   isplit 

open  to  show  plant- 


HOW  PLANTS  OBTAIN    THEIR  FOOD. 


103 


also  hard  and  shining  black,  splits  open  at  the  opposite  end,  that 
is  at  the  stem  end.     It  usually  splits 
open    in   the   form   of   three  ribs. 
Next   within  the  inner  coat   is   a 
very  thin,  whitish  film  (the  remains 
of  the  nucellus,  and  corresponding 
to  the  perisperm)  which  shrivels  up 
and  loosens  from  the  white  mass, 
the    endosperm,    within.      In    the 
castor-oil  bean,  then,  the  endosperm 
is  not  all  absorbed  by  the  embryo 
during  the  formation  of  the  seed. 
As    the    plant    becomes 
older  we  should  note  that 
the  fleshy  endosperm  be* 
comes  thinner  and  thin- 
ner,   and    at 
last    there    is 
nothing     but 


Fig.  93. 

How  the  garden  bean  comes  out  of  the  ground.  First  the  looped  hypocotyl, 
then  the  cotyledons  pulled  out,  next  casting  off  the  seed  coat,  last  the  plant  erect, 
bearing  thick  cotyledons,  the  expanding  leaves,  and  the  plumule  between  them. 

a  thin,  whitish  film  covering  the  green  faces  of  the  cotyledons. 
The  endosperm  has  been  gradually  absorbed  by  the  germinat- 
ing plant  through  its  cotyledons  and  used  for  food. 

Arisaema  triphyllum.* 

212.  Germination  of  seeds  of  jack-in-the-pulpit.— The  ovaries 
of  jack-in-the-pulpit  form  large,  bright  red  berries  with  a  soft 
pulp  enclosing  one  to  several  large  seeds.  The  seeds  are  oval  in 
form.  Their  germination  is  interesting,  and  illustrates  one  type 


*  In  lieu  of  Arisaema  make  a  practical  study  of  the  pea.     See  paragraph 
2i6a. 


104 


PHYSIOLOGY. 


of  germination  of  seeds  common  among  monocotyledonous  plants. 
If  the  seeds  are  covered  with  sand,  and 
kept  in  a  moist  place,  they  will  germi- 
nate readily. 

213.  How  the  embryo  backs  out  of 
the  seed. — The  embryo  lies  within  the 
mass  of  the  endosperm;  the  root  end, 
near  the  smaller  end  of  the 
seed.       The    club-shaped 
cotyledon    lies    near    the 


Fig.  94. 

Germination  of  castor-oil  bean. 


middle  of  the  seed,  surrounded  firmly  on  all  sides  by  the  endo- 
sperm. The  stalk,  or  petiole,  of  the  cotyledon,  like  the  lower 
part  of  the  petiole  of  the  leaves,  is  a  hollow  cylinder,  and 
contains  the  younger  leaves,  and  the  growing  end  of  the  stem 
or  bud.  When  germination  begins,  the  stalk,  or  petiole,  of  the 
cotyledon  elongates.  This  pushes  the  root  end  of  the  embryo 
out  at  the  small  end  of  the  seed.  The  free  end  of  the  embryo 
now  enlarges  somewhat,  as  seen  in  the  figures,  and  becomes  the 
bulb,  or  corm,  of  the  young  plant.  At  first  no  roots  are  visible, 
but  in  a  short  time  one,  two,  or  more  roots  appear  on  the  enlarged 
end. 

214.  Section  of  an  embryo.— If  we  make  a  longisection  of 
the  embryo  and  seed  at  this  time  we  can  see  how  the  club- 
shaped  cotyledon  is  closely  surrounded  by  the  endosperm. 
Through  the  cotyledon,  then,  the  nourishment  from  the  endo- 
sperm is  readily  passed  over  to  the  growing  embryo.  In  the 
hollow  part  of  the  petiole  near  the  bulb  can  be  seen  the  first 
leaf. 


HO W   PLANTS   OBTAIN    THEIR  FOOD. 


105 


Fig.  95. 

Seedlings  of  castor-oil  bean  casting  the  seed  coats,  and  showing  papery  rerm  ant 
of  the  endosperm. 


Fig.  96. 

Seedlings  of  jack-in-the- 
pulpit;  embryo  backing  out 
of  the  seed. 


Fig.  97- 

Section  of  germinating  embryos 
of  jack-in-the-pulpit,  showing  young 
leaves  inside  the  petiole  of  the 
cotyledon.  At  the  left  cotyledon 
shown  surrounded  by  the  endo- 
sperm in  the  seed;  at  right  endo- 
sperm removed  to  show  the  club- 
shaped  cotyledon. 


io6 


PHYSIO  LOG  Y. 


215.  How  the  first  leaf  appears. — As  the  embryo  backs  out 
of  the  seed,  it  turns  downward  into  the  soil,  unless  the  seed 
is  so  lying  that  it  pushes  straight 
downward.  On  the  upper  side  of 
arch  thus  formed,  in  the  petiole 
the  cotyledon,  a  slit  appears,  and 
through  thip  ~pening  the  first 
arches  its  way  out.  The  loop  of 
petiole  comes  out  first,  and  the 
later,  as  shown  in 
fig.  98.  The  petiole 
gradually 


the 
of 


leaf 
the 
leaf 


now 


Fig.  98.  Fig.  99.  Fig-  100. 

Seedlings  of  j ack-in-the-  Embryos     of     jack-in-the-pulpit  Seedling  of  jack:in- 

pulpit,  first  leaf   arching  still  attached  to  the  endosperm  in  the-pulpit;     section 

out  of  the  petiole  of  the  seed  coats,  and  showing  the  simple  of     the    endosperm 

cotyledon.  first  leaf.  and  cotyledon. 

straightens  up,  and  as  it  elongates  the  leaf  expands. 

216.  The  first  leaf  of  the  jack-in-the-pulpit  is  a  simple  one. 
— The  first  leaf  of  the  embryo  jack-in-the-pulpit  is  very  different 
in  form  from  the  leaves  which  we  are  accustomed  to  see  on 
mature  plants.  If  we  did  not  know  that  it  came  from  the  seed 


HOW  PLANTS  OBTAIN   THEIR  FOOD.  IO7 

of  this  plant  we  would  not  recognize  it.  It  is  simple,  that  is  it 
consists  of  one  lamina  or  blade,  and  not  of  three  leaflets  as  in 
the  compound  leaf  of  the  mature  plant.  The  simple  leaf  is 
ovate  and  with  a  broad  heart-shaped  base.  The  jack-in-the- 
pulpit,  then,  as  trillium,  and  some  other  monocotyledonous 
plants  which  have  compound  leaves  on  the  mature  plants,  have 
simple  leaves  during  embryonic  development.  The  ancestral 
monocotyledons  are  supposed  to  have  had  simple  leaves.  Thus 
there  is  in  the  embryonic  development  of  the  jack-in-the-pulpit, 
and  others  with  compound  leaves;  a  sort  of  recapitulation  of  the 
evolutionary  history  of  the  leaf  in  these  forms. 

216a.  Germination  of  the  pea. — Compare  with  the  bean. 
Note  especially  that  the  cotyledons  are  not  lifted  above  the  soil 
as  in  the  beans.  Compare  germination  of  acorns. 

Digestion. 

2166.  To  test  for  food  substance  in  the  seedlings  studied. — The  pumpkin, 
squash,  and  castor-oil  bean  are  examples  of  what  are  called  oily  seeds,  though 
flaxseed,  cotton-seed,  and  nuts  are  better.  Remove  a  small  portion  of  the 
substance  from  the  cotyledon  of  the  squash  and  crush  it  on  a  glass  slip  in 
a  drop  or  two  of  osmic  acid.*  Put  on  a  cover-glass  and  examine  with  the 
microscope.  The  black  amorphous  matter  shows  the  presence  of  oil  in  the 
protoplasm.  The  small  bodies  which  are  stained  yellow  are  aleurone 
grains,  a  form  of  protein  or  albuminous  substance.  Make  sections  of  the 
meat  of  a  Brazil  nut  or  hickory  nut  and  immerse  for  several  hours  in  ostiic 
acid.  They'  become  black  because  of  the  quantity  of  oil.  Mount  in 
water  and  examine  under  the  microscope.  The  oil  is  in  globules  which 
are  colored  black.  The  oil  is  converted  into  an  available  food  form  by 
the  action  of  an  enzyme  called  lipase,  which  splits  up  the  fatty  oil  into 
glucose  and  other  substances.  Lipase  has  been  found  in  the  endosperm  of 
the  castor  bean,  cocoanut,  and  in  the  cotyledons  of  the  pumpkin,  as  well 
as  in  other  seeds  containing  oil  as  a  stored  product.  The  aleurone  is  made 
available  by  an  enzyme  of  the  nature  of  trypsin. 

Test  the  cotyledon  of  the  bean  with  iodine  for  the  presence  of  starch.  If 
the  endosperm  of  corn  seed  has  not  been  tested  do  so  now  w!th  iodine. 
The  endosperm  consists  largely  of  starch.  The  starch  is  converted  to  glu- 

*  Dissolve  a  half  gram  of  osmic  acid  in  50  cc.  of  water  and  keep  tightl) 
corked  when  not  using. 


108  PHYSIO  LOG  Y. 

cose  by  a  diastatic  " ferment"  formed  by  the  seedling  as  it  germinates. 
Make  a  thin  cross-section  of  a  grain  of  wheat,  including  the  seed  coat  and  a 
portion  of  the  interior,  treat  with  iodine  and  mount  for  microscopic  exam- 
ination. Note  the  abundance  of  search  in  the  internal  portion  of  endo- 
sperm. Note  a  layer  of  cells  on  the  outside  of  the  starch  portions  filled 
with  small  bodies  which  stain  yellow.  These  are  aleurone  grains.  The 
cellulose  in  the  cell  walls  of  the  endosperm  is  dissolved  by  another  enzyme 
called  cytase,  and  some  plants  store  up  cellulose  for  food.  For  example,  in 
the  endosperm  of  the  date  the  cell  walls  are  very  much  thickened  and  pitted. 
The  cell  walls  consist  of  reserve  cellulose  and  the  seedling  makes  use  of  it 
for  food  during  growth. 

216c.  Albuminous  and  exalbuminous  seeds. — In  seeds  where  the  food  is 
stored  outside  of  the  embryo  they  are  called  albuminous;  examples,  corn, 
wheat  and  other  cereals,  Indian  turnip,  etc.  In  those  seeds  where  the  food 
is  stored  up  in  the  embryo  they  are  called  exalbuminous;  examples,  bean, 
pea,  pumpkin,  squash,  etc. 

217.  Digestion  has  a  well-defined  meaning  in  animal  physiology  and 
relates  to  the  conversion  of  solid  food,  usually  within  the  stomach,  into  a 
soluble  form  by  the  action  of  certain  gastric  juices,  so  that  the  liquid  food 
may  be  absorbed  into  the  circulatory  system.  The  term  is  not  often  ap- 
plied in  plant  physiology,  since  the  method  of  obtaining  food  is  in  general 
fundamentally  different  in  plants  and  animals.  It  is  usually  applied  to 
the  process  of  the  conversion  of  starch  into  some  form  of  sugar  in  solution, 
as  glucose,  etc.  This  we  have  found  takes  place  in  the  leaf,  especially  at 
night,  through  the  action  of  a  diastatic  ferment  developed  more  abundantly 
in  darkness.  As  a  result,  the  starch  formed  during  the  day  in  the  leaves  is 
digested  at  night  and  converted  into  sugar,  in  which  form  it  is  transferred 
to  the  growing  parts  to  be  employed  in  the  making  of  new  tissues,  or  it  is 
stored  for  future  use;  in  other  cases  it  unites  with  certain  inorganic  sub- 
stances, absorbed  by  the  roots  and  raised  to  the  leaf,  to  form  proteids  and 
other  organic  substances.  In  tubers,  seeds,  parts  of  stems  or  leaves  where 
starch  is  stored,  it  must  first  be  "digested"  by  the  action  of  some  enzyme 
before  it  can  be  used  as  food  by  the  sprouting  tubers  or  germinating  seeds. 

For  example,  starch  is  converted  to  a  glucose  by  the  action  of  a  diastase. 
Cellulose  is  converted  to  a  glucose  by  cytase.  Albuminoids  are  converted 
*  into  available  food  by  a  tryptic  ferment.  Fatty  oils  are  converted  into 
glucose  and  other  products  by  lipase. 

Inulin,  a  carbohydrate  closely  related  to  starch,  is  stored  up  for  food  in 
solution  in  many  composite  plants,  as  in  the  artichoke,  the  root  tuber  of 
dahlia,  etc.  When  used  for  food  by  the  growing  plant  it  is  converted  into 
glucose  by  an  enzyme,  inulase.  Make  a  section  of  a  portion  of  a  dahlia 
root  and  immerse  in  95%  alcohol  for  several  hours.  The  inulin  is  precipi- 
tated into  sphEero  crystals.  (See  also  paragraphs  156-161  and  2166.) 


HOW  PLANTS   OBTAIN    THEIR  FOOD.  109 

218.  Then  there  are  certain  fungi  which  feed  on  starch  or  other  organic 
substances  whether  in  the  host  or  not,  which  excrete    certain  enzymes  to 
dissolve  the  starch,  etc.,  to  bring  it  into  a  soluble  form  before  they  can 
absorb  it  as  food.     Such  a  process  is  a  sort  of  extracellular  digestion,  i.e., 
the  organism  excretes  the  enzyme  and  digests  the  solid  outside,  since  it 
cannot  take  the  food  within  its  cells  in  the  solid  form.     To  a  certain  degree 
the  higher  plants  perform  also  extracellular  digestion  in  the  action  of  root- 
hair  excretion  on  insoluble  substances,  and  in  the  case  of  the  humus  sapro- 
phytes.    But  for  them  soluble  food  is  largely  prepared  by  the  action  of 
acids,  etc.,  in  the  soil  or  water,  or  by  the  work  of  fungi  and  bacteria  as 
described  in  Chapter  9. 

219.  Assimilation. — In  plant  physiology  the  term  assimilation  has  been 
chiefly  used  for  the  process  of  carbon-dioxide  assimilation   (=  photosyn- 
thesis).    Some  objections  have  been  raised  against  thje  use  of  assimilation 
here  as  one  of  the  life  processes  of  the  plant,  since  its  inception  stages  are 
due  to  the  combined  action  of  light,  an  external  factor,  and  chlorophyll  in 
the  plant  along  with  the  living  chloroplastid.     So  long,  however,  as  it  is 
not  known  that  this  process  can  take  place  without  the  aid  of  the  living 
plant,  it  does  not  seem  proper  to  deny  that  it  is  altogether  not  a  process  of 
assimilation.     It  is  not  necessary  to  restrict  the  term  assimilation  to  the 
formation  of  new  living  matter  in  the  plant  cell;  it  can  be  applied  also  to 
the  synthetic  processes  in  the  formation  of  carbohydrates,  proteids,  etc., 
and  called  synthetic  assimilation.     The  sun  supplies  the  energy,  which  is 
absorbed  by  the  chlorophyll,  for  splitting  up  the  carbonic  acid,  and  the 
living  chloroplast  then  assimilates  by  a  synthetic  process  the  carbon,  hydro- 
gen, and  oxygen.     This  process  then  can  be  called  photo  synthetic  assimi- 
lation.    The  nitrite  and  nitrate  bacteria  derive  energy  in  the  process  of 
nitrification ,.  which  enables  them  to  assimilate  CO2  from  the  air,  and  this  is 
called   chemo synthetic  assimilation.     The  inorganic   material   in   the  form 
of  mineral  salts,  nitrates,  etc.,  absorbed  by  the  root,  and  carried  up  to  the 
leaves,  here  meets  with  the  carbohydrates  manufactured  in  the  leaf.     Under 
the  influence  of  the  protoplasm  synthesis  takes  place,  and  proteids  and 
other  organic  compounds  are  built  up  by  the  union  of  the  salts,  nitrates, 
etc.,  with  the  carbohydrates.     This  is  also  a  process  of  synthetic  assimila- 
tion.    These  are  afterward  stored  as  food,  or  assimilated  by  the  proto- 
plasm in  the  making  of  new  living  matter,  or  perhaps  without  the  first 
process  of  synthetic  assimilation  some  of  the  inorganic  salts,  nitrates,  and 
carbohydrates  meeting  in  the  protoplasm  are  assimilated  into  new  living 
matter  directly. 


CHAPTER  XI. 

RESPIRATION. 

220.  One  of  the  life  processes  in  plants  which  is  extremely 
interesting,  and  which  is  exactly  the  same  as  one  of  the  life  proc- 
esses of  animals,  is  easily  demonstrated  in  several  ways. 

221.  Simple  experiment  to  demonstrate  the  evolution   of 
C02  during  germination. — Where  there  are  a  number  of  stu- 
dents and  a  number  of  large  cylinders  are  not 
at  hand,  take  bottles  of  a  pint  capacity  and 
place  in  the  bottom  some  peas  soaked  for  12  to 
24  hours.     Cover  with  a  glass  plate  which  has 
been  smeared  with  vaseline  to  make  a  tight 
joint  with  the  mouth  of  the  bottle.     Set  aside 
in  a  warm  place  for   24  hours.     Then  slide 
the  glass  plate  a  little  to  one  side  and  quickly 
pour  in  a  little  baryta  water  so  that  it  will  run 
down  on  the  inside  of  the  bottle.     Cover  the 
bottle  again.     Note  the  precipitate  of  barium 
carbonate  which  demonstrates  the  presence  of 

Pig.  101.  e  r 

Test  for  presence  of  CO   in  the  bottle.     Lower  a  lighted  taper.     It 

carbon  dioxide  in  ves-    .  .          •  i      j    r  r  ,1  .•, 

sei  with  germinating  is  extinguished  because  of  the  great  quantity 
of  CO2.  If  flower  buds  are  accessible,  place 
a  small  handful  in  each  of  several  jars  and  treat  the  same  as  in 
the  case  of  the  peas.  Young  growing  mushrooms  are  excellent 
also  for  this  experiment,  and  serve  to  show  that  respiration  takes 
place  in  the  fungi. 

no 


RESPIRA  TION. 


Ill 


222.  If  we  now  take  some  of  the  baryta  water  and  blow  our 
" breath"  upon  it  the  same  film  will  be  formed.     The  carbon 
dioxide  which  we  exhale  is  absorbed  by  the  baryta  water,  and 
forms  barium  carbonate,  just  as  in  the  case  of  the  peas.     In  the 
case  of  animals  the  process  by  which  oxygen  is  taken  into  the 
body  and  carbon  dioxide  is  given  off  is  respiration.     The  process 
in  plants  which  we  are  now  studying  is  the  same,  and  also  is  res- 
piration.    The  oxygen  in  the  vessel  was  partly  used  up  in  the 
process,  and  carbon  dioxide  was  given  off.     (It  will  be  seen  that 
this  process  is  exactly  the  opposite  of  that  which  takes  place  in 
carbon-dioxide  assimilation.) 

223.  To  show  that  oxygen  from  the  air  is  used  up  while 
plants   respire. — Soak   some   wheat   for    24    hours    in    water. 
Remove  it  from  the  water  and  place 

it  in  the  folds  of  damp  cloth  or 
paper  in  a  moist  vessel.  Let  it 
remain  until  it  begins  to  germinate. 
Fill  the  bulb  of  a  thistle  tube  with 
the  germinating  wheat.  By  the  aid 
of  a  stand  and  clamp,  support  the 
tube  upright,  as  shown  in  fig.  102. 
Let  the  small  end  of  the  tube  rest 
in  a  strong  solution  of  caustic  potash 
(one  stick  caustic  potash  in  two- 
thirds  tumbler  of  water)  to  which 
red  ink  has  been  added  to  give  a 
deep  red  color.  Place  a  small  glass 
plate  over  the  rim  of  the  bulb  and 
seal  it  air-tight  with  an  abundance 
of  vaseline.  Two  tubes  can  be  set 
up  in  one  vessel,  or  a  second  one 
can  be  set  up  in  strong  baryta  water 
colored  in  the  same  way. 

224.  The  result. — It  will  be  seen  that  the  solution  of  caustic 
potash  rises  slowly  in  the  tube;    the  baryta  water  will  also,  if 
that  is  used.     The  solution  is  colored  so  that  it  can  be  plainly 


Fig.  1 02. 

Apparatus  to  show  respiration  of 
germinating  wheat. 


112 


PHYS1OLOG  Y. 


seen  at  some  distance  from  the  table  as  it  rises  in  the  tube.  In 
the  experiment  from  which  the  figure  was  made  for  the  accom- 
panying illustration,  the  solution  had  risen 
in  6  hours  to  the  height  shown  in  fig.  102. 
In  24  hours  it  had  risen  to  the  height  shown 
in  fig.  103. 

225.  Why    the    solution    of    caustic 
potash  rises  in  the  tube. — Since  no  air  can 
get  into  the  thistle    tube  from   above    or 
below,  it  must  be  that   some  part  of  the 
air  which  is  inside  of  the  tube  is  used  up 
while   the  wheat    is    germinating.      From 
our  study  of  germinating  peas,  we  know 
that  a  suffocating  gas,  carbon  dioxide,  is 
given   off  while    respiration    takes   place. 
The  caustic  potash  solution,  or  the  baryta 
water,  whichever  is  used,  absorbs  the  car- 
bon dioxide.     The  carbon  dioxide  is  heavier 
than  air,  and  so  it  settles  down  in  the  tube 
where  it  can  be  absorbed. 

226.  Where  does  the   carbon  dioxide 
come  from? — We  know  it  comes  from  the 

growing  seedlings.  The  symbol  for  carbon  dioxide  is  CO2.  The 
carbon  comes  from  the  plant,  because  there  is  not  enough  in 
the  ah-.  Nitrogen  could  not  join  with  the  carbon  to  make  CC>2. 
Some  oxygen  from  the  air  or  from  the  protoplasm  of  the  grow- 
ing seedlings  (more  probably  the  latter)  joins  with  some  of  the 
carbon  of  the  plant.  These  break  away  from  their  association 
with  the  living  substance  and  unite,  making  CO2-  The  oxygen 
absorbed  by  the  plant  from  the  air  unites  with  the  living  sub- 
stance, or  perhaps  first  with  food  substances,  and  from  these  the 
plant  is  replenished  with  carbon  and  oxygen.  After  the  demon- 
stration has  been  made,  remove  the  glass  plate  which  seals  the 
thistle  tube  above,  and  pour  in  a  small  quantity  of  baryta  water. 
The  white  precipitate  formed  affords  another  illustration  that 
carbon  dioxide  is  released. 


Fig.  103. 

Apparatus  to  show 
respiration  of  germinat- 
ingwheat. 


RESPIRA  TION. 


227.  Respiration  is  necessary  for  growth. — After  performing  experiment  in 
paragraph  221,  ii  the  vessel  has  not  been  open 
too  long  so  that  oxygen  has  entered,  we  may  use 
the  vessel  for  another  experiment,  or  set  up  a 
new  one  to  be  used  in  the  course  of  12  to  24 
hours,  after  some  oxygen  has  been  consumed. 
Place  some  folded  damp  filter  paper  on  the 
germinating  peas  in  the  jar.  Upon  this  place 
one-half  dozen  peas  which  have  just  been 

germinated,  and  in  which  the  roots  are  about  F^;  I04- 

,  _,  ,    ,       ,  ,  ,  ,        rea  seedlings ;  the  one 

20-25  mm  long.     The  vessel  should  be  covered  at  the  left  had  no  oxygen 

tightly  again  and  set  aside  in  a  warm  room.  ^"^onlTtheS 
A  second  jar  with  water  in  the  bottom  instead  in   oxygen   and  growth 

.       ,  .  ,  was  evident. 

of  the  germinating  peas  should  be  set  up  as  a 

check.     Damp  folded  filter  paper  should  be  supported  above  the  water, 

and  on  this  should  be  placed  one- 
half  dozen  peas  with  roots  of  the 
same  length  as  those  in  the  jar 
containing  carbon  dioxide. 

228.  In  24  hours  examine  and 
note  how  much  growth  has  taken 
place.     It  will  be  seen  that  the 
roots  have  elongated  but  very  little 
or  none  in  the  first  jar,  while  in 
the  second  one  we  see  that  the 
roots    have    elongated    consider- 
ably, if  the  experiment  has  been 
carried  on  carefully.     Therefore 
in  an  atmosphere  devoid  of  oxygen 
very  little  growth  will  take  place, 
which  shows  that  normal  respira- 
tion with  access  of  oxygen  (aerobic 
respiration)  is  necessary  for  growth 

229.  Another  way  of  perform- 


Fig. 105. 

Experiment  to  show  that  growth  takes 
place  more  rapidly  in  presence  of  oxygen 
than  in  absence  of  oxygen.  The  two  tubes 
in  the  vessel  represent  the  condition  at  the 
beginning  of  the  experiment.  At  the  close 
of  the  experiment  the  roots  in  the  tube  at 
the  left  were  longer  than  those  in  the  tube 
filled  at  the  start  with  mercury.  The  tube 


ing  the  experiment. — If  we  wish 
we  may  use  the  following  experi- 
ment instead  of  the  simple  one 
indicated  above.  Soak  a  handful 


niieu  at  Liie  stitu  WXLII  mcn-m  j.  uv»~~          f  •  t  u    ,,_0 

outside  of  the  vessel  represents  the  condi-      of  peas  in  water  for   12-24  hours, 

2ZAft££&  SaSTSflSS.  %£     ^  S*™™«  ~  that  twelve  with 

off  has  displaced  a  portion  of  the  mercury.      ^e  radides   20-25  mm  long  may 
This  also  shows  anaerobic  respiration.  " 

be  selected.     Fill  a  test  tube  with 

mercury  and  carefully  invert  it  in  a  vessel  of  mercury  so  that  there  will 


114  PHYSIOLOGY. 

be  no  air  in  the  upper  end.  Now  nearly  fill  another  tube  and  invert  in  the 
same  way.  In  the  latter  there  will  be  some  air.  Remove  the  outer  coats 
from  the  peas  so  that  no  air  will  be  introduced  in  the  tube  filled  with  the 
mercury,  and  insert  them  one  at  a  time  under  the  edge  of  the  tube  beneath 
the  mercury,  six  in  each  tube,  having  first  measured  the  length  of  the  radicles. 
Place  in  a  warm  room.  In  24  hours  measure  the  roots.  Those  in  the  air 
will  have  grown  considerably,  while  those  in  the  other  tube  will  have  grown 
but  little  or  none. 

230.  Anaerobic  respiration. — The  last  experiment  is  also  an  excellent 
one  to  show  anaerobic  respiration.    In  the  tube  filled  with  mercury  so  tha; 
when  inverted  there  will  be  no  air,  it  will  be  seen  after  24  hours  that  a  gas 
has  accumulated  in  the  tube  which  has  crowded  out  some  of  the  mercury. 
With  a  wash  bottle  which  has  an  exit  tube  properly  curved,  some  water 
may  be  introduced  in  the  tube.    Then  insert  underneath  a  small  stick  of 
caustic  potash.    This  will  form  a  solution  of  potash,  and  the  gas  will  be 
partly  or  completely  absorbed.     This  shows  that  the  gas  was  carbon  di- 
oxide.   This  evolution  of  carbon  dioxide  by  living  plants  when  there  is  no 
access  of  oxygen  is  anaerobic  respiration  (sometimes  called  intramolecular 
respiration).     It  occurs  to  a  marked  extent  in  the  yeast  plant. 

231.  Energy  set  free  during  respiration. — From  what  we  have  learned  of 
the  exchange  of  gases  during  respiration  we  infer  that  the  plant  loses  carbon 
during  this  process.     If  the  process  of  respiration  is  of  any  benefit  to  the 
plant,  there  must  be  some  gain  in  some  direction  to  compensate  the  plant 
for  the  loss  of  carbon  which  takes  place. 

It  can  be  shown  by  an  experiment  that  during  respiration  there  is  a 
slight  elevation  of  the  temperature  in  the  plant  tissues.  The  plant  then 
gains  some  heat  during  respiration.  Energy  is  also  manifested  by  growth. 

232.  Bespiration  in  a  leafy  plant. — We  may  take  a  potted  plant  which 
has  a  well-developed  leaf  surface  and  place  it  under  a  tightly  fitting  bell  jar. 

Under  the  bell  jar  there  also  should  be  placed 
a  small  vessel  containing  baryta  water.  A  sim- 
ilar apparatus  should  be  set  up,  but  with  no 
plant,  to  serve  as  a  check.  The  experiment  must 
be  set  up  in  a  room  which  is  not  frequented  by 
persons,  or  the  carbon  dioxide  in  the  room  from 
respiration  will  vitiate  the  experiment.  The  bell 
jar  containing  the  plant  should  be  covered  with 
a  black  cloth  to  prevent  carbon  assimilation.  In 

Test  for  Hberation  of  car-  the  course  of  IO  or  I2  hours>  if  everything  has 
bon  dioxide  from  leafy  plant  worked  properly,  the  baryta  water  under  the  jar 
during  respiration.  Baryta  .,,  ,  -ni  1^1  r-L- 

water     in     smaller     vessel,  with  the  plant  will  show  the  film  of  barium  car- 

(Sachs.)  bonate,  while  the  other  one  will  show  none.     Res- 

piration, therefore,  takes  place  in  a  leafy  plant  as  well  as  in  germinating  seed* 


RESPIRA  TION. 


233.  Respiration  in  fungi. — If  several  large  actively  growing  mushrooms 
are  accessible,  place  them  in  a  tall  glass  jar  as  described  for  determining 
respiration  in  germinating  peas.     In  the  course  of  12  hours  test  with  the 
lighted  taper  and  the  baryta  water.     Respiration  takes  place  in  fungi  as 
well  as  in  green  plants. 

234.  Respiration  in  plants  in  general. — Respiration  is  general  in   all 
plants,   though  not  universal.     There  are  some  exceptions  in  the  lower 
plants,  notably  in  certain  of  the  bacteria,  which  can  only  grow  and  thrive 
in  the  absence  of  oxygen. 

235.  Respiration  a  breaking-down  process. — We  have  seen  that  in  res- 
piration the  plant  absorbs  oxygen  and  gives  off  carbon  dioxide.     We  should 
endeavor  to  note  some  of  the  effects  of  respiration  on  the  plant.     Let  us 
take,  say,  two  dozen  dry  peas,  weigh  them,  soak  for  12-24  hours  in  water, 
and,  in  the  folds  of  a  cloth  kept  moist  by  covering  with  wet  paper  or  sphag- 
num, germinate  them.     When  well  germinated  and  before  the  green  color 
appears  dry  well  in  the  sun,  or  with  artificial  heat,  being  careful  not  to  burn 
or  scorch  them.     The  aim  should  be  to  get  them  about  as  dry  as  the  seed 
were  before  germination.      Now  weigh.      The 

germinated  seeds  weigh  less  than  the  dry  peas. 
There  has  then  been  a  loss  of  plant  substance 
during  respiration. 

236.  Fermentation  of  yeast. — Take  two  fer- 
mentation tubes.     Fill  the  closed  tubular  parts 
of  each  with  a  weak  solution  of  grape  sugar,  or 
with  potato    decoction,  leaving   the   open   bulb 
nearly  empty.     Into   the    liquid    of  one  of   the 
tubes  place  a  piece  of  compressed  yeast  as  large 
as  a  pea.     If  the  tubes  are  kept  in  a  warm  place 
for   24  hours   bubbles   of  gas   may  be   noticed 
rising  in  the  one  in  which  the  yeast  was  placed, 
while  in  the  second  tube  no  such  bubbles  appear, 
especially  if  the  filled  tubes  are  first  sterilized. 
The  tubes  may  be  kept  until  the  first  is  entirely 
filled  with  the  gas.     Now  dissolve  in  the  liquid 
a   small    piece    of  caustic   potash.      Soon   the 
gas  will  begin   to  be   absorbed,  and  the  liquid 
will  rise  until  it  again  fills  the  tube.     The  gas 

was  carbon    dioxide,    which    was   chiefly  pro-  Fig.  107. 

duced  during  the  anaerobic  respiration  of  the         Fermentation  tube  with 

°  culture  of  yeast, 

rapidly  growing  yeast  cells.      In  bread  making 

this  gas  is  produced  in  considerable  quantities,  and  rising  through  the 
dough  fills  it  with  numerous  cavities  containing  gas,  so  that  the  breau 
"rises."  When  it  is  baked  the  heat  causes  the  gas  in  the  cavities  to  ex- 


u6 


PHYSIOLOGY. 


pand  greatly.  This  causes  the  bread  to  "rise"  more,  and  baked  in 
this  condition  it  is  "light."  There  are  two  special  processes  accom- 
panying the  fermentation  by  yeast:  ist,  the  evolution  of  carbon  dioxide 
as  shown  above;  and,  2d,  the  formation  of  alcohol.  The  best  illus- 
tration of  this  second  process  is  the  brewing  of  beer,  where  a  form  of 
the  same  organism  which  is  employed  in  "bread  rising"  is  used  to  "brew 
beer." 

237.  The  yeast  plant. — Before  the  caustic  potash  is  placed  in  the  tube 
some  of  the  fermented  liquid  should  be  taken  for  study  of  the  yeast  plant, 
unless  separate  cultures  are  made  for  this  pur- 
pose.     Place  a   drop   of   the  fermented  liquid 
on  a  glass  slip,  place  on  this  a  cover-glass,  and 
examine  with  the  microscope.     Note  the  min- 
ute oval  cells  with  granular  protoplasm.     These 
are  the  yeast  plant.      Note  in  some  a  small 
"bud"  at   one   side  of  the  end.     These  buds 
increase  in  size   and  separate  from  the  parent 
plant.      The    yeast    plant  is    one  celled,  and 
multiplies  by  "budding" 
or  "sprouting."     It   is  a 
fungus,  and  some  species 
of  yeast  like  the  present 
one  do  not  form  any  my- 
celium.       Under    certain 
conditions,  which  are  not 

very  favorable  for  growth 
Fig.  io8a.  ,     J       . 

Yeast.  Saccharo-  (examPle>  when  the  yeast  is 
myces  ceriviseae.  a,  grown  in  a  weak  nutrient 
small  colony;  b,  single  ,  ,  . 

cell  budding;  c,  single  substance  on  a  thin  layer 

ssflsvsjr'*  °f  a  p'aster  parfs  siab>. 

spores   free    from  the  several  spores  are  formed 
ascus.     (AfterRees.)     . 

in  many  of  the  yeast  cells. 


Fig.  1 08. 

Fermentation  tube  filled 
with  CC>2  from  action  of 
yeast  in  a  sugar  solution. 


After  a  period  of  rest  these  spores,  will  sprout  and  produce  the  yeast  plant 
again.  Because  of  this  peculiar  spore  formation  some  place  the  yeast 
among  the  sac  fungi.  (See  classification  of  the  fungi.) 

238.  Organized  ferments  and  unorganized  ferments. — An  organism 
like  the  yeast  plant  which  produces  a  fermentation  of  a  liquid  with  evo- 
lution of  gas  and  alcohol  is  sometimes  called  a  ferment,  or  ferment  or- 
ganism, or  an  organized  ferment.  On  the  other  hand  the  diastatic  fer- 
ments or  enzymes  like  diastase,  taka  diastase,  animal  diastase  (ptyalin  in 
the  saliva),  cytase,  etc.,  are  unorganized  ferments.  In  the  case  of  these 
it  is  better  to  say  enzyme  and  leave  the  word  ferment  for  the  ferment 
organisms. 


RES  P  IK  A  TION. 


117 


239.  Importance  of  green  plants  in  maintaining  purity  of  air. — By  respi- 
ration, especially  of  animals,  the  air  tends  to  become  "  foul  "  by  the  increase 
of  CO2.  Green  plants,  i.e.,  plants  with  chlorophyll,  purify  the  air  during 
photosynthesis  by  absorbing  CO2  and  giving  off  oxygen.  Animals  absorb 
in  respiration  large  quantities  of  oxygen  and  exhale  large  quantities  of  CO2 
Plants  absorb  a  comparatively  small  amount  of  oxygen  in  respiration  and 
give  off  a  comparatively  small  amount  of  CO2.  But  they  absorb  during 
photosynthesis  large  quantities  of  CO2and  give  off  large  quantities  of  oxygen. 
In  this  way  a  balance  is  maintained  between  the  two  processes,  so  that  the 
percentage  ofCO2in  the  air  remains  approximately  the  same,  viz.,  about 
four- tenths  of  one  per  cent,  while  there  are  approximately  21  parts  oxygen 
and  79  parts  nitrogen 

239a.  Comparison  of  respiration  and  photosynthesis. 

Carbon  dioxide  is  taken  in  by  the  plant  and  oxygen 
is  liberated. 

Starch  is  formed  as  a  result  of  the  metabolism,  or 
chemical  change. 

The  process  takes  place  only  in  green  plants,  and  in 
the  green  parts  of  plants,  that  is,  in  the  presence 
of  the  chlorophyll.  (Exception  in  purple  bacte- 
rium. ) 

The  process  only  takes  place  under  the  influence  oi 
sunlight. 

It  is  a  building-up  process,  because  new  plant  sub- 
stance is  formed. 

Oxygen  is  taken  in  by  the  plant  and  carbon  dioxide 
is  liberated. 

Carbon  dioxide  is  formed  as  a  result  of  the  meta- 
bolism, or  chemical  change. 

The  process  takes  place  in  all  plants  whether  they 

Respiration.  \  possess  chlorophyll  or  not  (exceptions  in  anaerobic 

bacteria). 

The  process  takes  place  in  the  dark  as  well  as  in 
the  sunlight. 

It  is  a  breaking-down  process,  because  disintegra- 
tion of  plant  substance  occurs. 


Starch  formation  or 
Photosynthesis. 


CHAPTER   XII. 

GROWTH. 

By  growth  is  usually  meant  an  increase  in  the  bulk  of  the 
plant  accompanied  generally  by  an  increase  in  plant  sub- 
stance. Among  the  lower  plants  growth  is  easily  studied  ir. 
some  of  the  fungi. 

240.  Growth  in  mucor. — Some  of  the  gonidia  (often  called 
spores)   may  be  sown  in  nutrient  gelatine  or  agar,  or  even  in 
prune  juice.      If  the  culture  has  been  placed  in  a  warm  room,  in 
the  course  of  24  hours,  or  even  less,  the  preparation  will  be  ready 
for  study. 

241.  Form  of  the  gonidia. — It  will  be  instructive  if  we  first 
examine  some  of  the  gonidia  which  have  not  been  sown  in  the  cul- 
ture medium.      We  should  note  their  rounded  or  globose  form,  as 
well  as  their  markings  if  they  belong  to  one  of  the  species  with 
spiny  walls.      Particularly  should  we  note  the  size,  and  if  possible 
measure  them  with  the  micrometer,  though  this  would  not  be 
absolutely  necessary  for  a  comparison,  if  the  comparison  can  be 
made  immediately.      Now  examine  some  of  the  gonidia  which 
were  sown  in  the  nutrient  medium.      If  they  have  not  already 
germinated  we  note  at  once  that   they  are  much   larger   than 
those  which  have  not  been  immersed  in  a  moist  medium. 

242.  The  gonidia  absorb  water  and  increase  in  size  before 
germinating. — From  our  study  of  the  absorption  of  water  or 
watery  solutions  of  nutriment  by  living  cells,  we  can  easily  un- 
derstand the  cause  of  this  enlargement  of  the  gonidium  of  the 
mucor  when  surrounded  by   the  moist  nutrient  medium.     The 
cell -sap  in  the  spore  takes  up  more  water  than  it  loses  by  diffu- 

118 


GROWTH.  IIQ 

sion,  thus  drawing  water  forcibly  through  the  protoplasmic  mem- 
brane.    Since    it    does    not    filter    out    readily,  the  increase  in 


Fig.  109. 
Spores  of  mucor,  and  different  stages  of  germination. 

quantity  of  the  water  in  the  cell  produces  a  pressure  from  within 
which  stretches  the  membrane,  and  the  elastic  cell  wall  yields. 
Thus  the  gonidium  becomes  larger. 

243.  How  the  gonidia  germinate. — We  should  find  at  this 
time  many  of  the  gonidia  extended  on  one  side  into  a  tube-like 
process  the  length  of  which  varies  according  to  time  and  tempera- 
ture.     The  short  process  thus  begun  continues  to  elongate.     This 
elongation  of  the  plant  is  growth,  or,  more  properly  speaking,  one 
of  the  phenomena  of  growth. 

244.  The  germ  tube  branches  and  forms  the  mycelium. — 
In  the  course  of  a  day  or  so  branches  from  the  tube  will  appear. 
This   branched   form   of  the   threads   of  the  fungus  is,  as  we 
remember,   the  mycelium.     We  can  still  see  the  point  where 
growth  started  from  the  gonidium.      Perhaps  by  this  time  several 
tubes  have  grown  from  a  single  one.      The  threads  of  the  myce- 
lium near  the  gonidium,  that  is,  the  older  portions  of  them,  have 
increased  in  diameter  as  they  have  elongated,  though  this  increase 
in  diameter  is  by  no  means  so  great  as  the  increase  in  length. 
After  increasing  to  a  certain  extent  in  diameter,  growth  in  this 
direction  ceases,  while  apical  growth  is  practically  unlimited, 
being  limited  only  by  the  supply  of  nutriment. 

245.  Growth  in  length  takes  place  only  at  the  end  of  the 
thread. — If  there  were  any  branches  on  the  mycelium  when  the 


120  PHYSIOLOGY. 

culture  was  first  examined,  we  can  now  see  that  they  remain 
practically  the  same  distance  from  the  gonidium  as  when  they 
were  first  formed.  That  is,  the  older  portions  of  the  mycelium 
do  not  elongate.  Growth  in  length  of  the  mycelium  is  confined 
to  the  ends  of  the  threads. 

246.  Protoplasm    increases    by  assimilation  of    nutrient 
substances. — As  the  plant  increases  in  bulk  we  note  that  there 
is  an   increase   in  the   protoplasm,  for  the  protoplasm  is   very 
easily  detected  in  these  cultures  of  mucor.     This  increase  in  the 
quantity  of  the  protoplasm  has  come  about  by  the  assimilation 
of  the  nutrient  substance,  which   the  plant  has  absorbed.     The 
increase  in  the  protoplasm,  or  the  formation  of  additional  plant 
substance,  is  another  phenomenon  of  growth  quite  different  from 
that  of  elongation,  or  increase  in  bulk. 

247.  Growth  of  roots. — For  the  study  of  the  growth  of  roots 
we  may  take  any  one  of  many  different  plants.     The  seedlings  of 
such  plants  as  peas,  beans,   corn,  squash,  pumpkin,  etc.,  serve 
excellently  for  this  purpose. 

248.  Roots  of  the  pumpkin. — The  seeds,  a  handful  or  so,  are 
soaked  in  water  for  about   12  hours,  and  then  placed  between 
layers  of  paper  or  between  the  folds  of  cloth,  which  must  be  kept 
quite  moist  but  not  very  wet,  and  should  be  kept  in  a  warm  place. 
A  shallow  crockery  plate,  with  the  seeds  lying  on  wet  filter  paper, 
and  covered  with  additional  filter  paper,  or  with  a  bell  jar,  an- 
swers the  purpose  well. 

The  primary  or  first  root  (radicle)  of  the  embryo  pushes  its  way 
out  between  the  seed  coats  at  the  small  end.  When  the  seeds  are 
well  germinated,  select  several  which  have  the  root  \-$cm  long. 
With  a  crow-quill  pen  we  may  now  mark  the  terminal  portion  of 
the  root  off  into  very  short  sections  as  in  fig.  no.  The  first  mark 
should  be  not  more  than  \mm  from  the  tip,  and  the  others  not 
more  than  imm  apart.  Now  place  the  seedlings  down  on  damp 
filter  paper,  and  cover  with  a  bell  jar  so  that  they  will  re- 
main moist,  and  if  the  season  is  cold  place  them  in  a  warm  room. 
At  intervals  of  8  or  10  hours,  if  convenient,  observe  them  and 
note  the  farther  growth  of  the  root. 


GROWTH. 


121 


249.  The  region  of  elongation. — While  the  root  has  elon- 
gated, the  region  of  elongation  is  not  at  the  tip  of  the  root.    It  lies 
a  little  distance  back  from  the  tip,  beginning  at 
about  2mm  from  the  tip  and  extending  over 
an  area  represented  by  from  4-5  of  the  milli- 
meter   marks.         The 
root  shown  in  fi^.  no 
was  marked  at  IOA.M. 
on  July  5.     At  6  P.M. 
of  the    same    day,    8 


Fig.  no. 

Root  of  germinating  pumpkin,  showing  region  of 
elongation  just  back  of  the  tip. 


hours  later,  growth  had  taken  place  as  shown  in  the  middle 
figure.  At  9  A.M.  on  the  following  day,  15  hours  later,  the 
growth  is  represented  in  the  lower  one.  Similar  experiments 
upon  a  number  of  seedlings  give  the  same  result :  the  region  of 
elongation  in  the  growth  of  the  root  is  situated  a  little  distance 
back  from  the  tip.  Farther  back  very  little  or  no  elongation 
takes  place,  but  growth  in  diameter  continues  for  some  time,  as 
we  should  discover  if  we  examined  the  roots  of  growing  pump- 
kins, or  other  plants,  at  different  periods. 

250.  Movement  of  region  of  greatest  elongation. — In  the 
region  of  elongation  the  areas  marked  off  do  not  all  elongate 
equally  at  the  same  time.  The  middle  spaces  elongate  most 
rapidly  and  the  spaces  marked  off  by  the  6,  7,  and  8  mm  marks 
elongate  slowly,  those  farthest  from  the  tip  more  slowly  than  the 
others,  since  elongation  has  nearly  ceased  here.  The  spaces 
marked  off  between  the  2-^mm  marks  also  elongate  slowly,  but 
soon  begin  to  elongate  more  rapidly,  since  that  region  is  becom- 
ing the  region  of  greatest  elongation.  Thus  the  region  of  greatest 
elongation  moves  forward  as  the  root  grows,  and  remains  ap- 
proximately at  the  same  distance  behind  the  tip. 

251.  Formative  region. — If  we  make  a  longitudinal  section  of  the  tip  of  a 
growing  root  of  the  pumpkin  or  other  seedling,  and  examine  it  with  the  mi- 


122  PHYSIOLOGY. 

croscope,  we  see  that  there  is  a  great  difference  in  the  character  of  the 
cells  of  the  tip  and  those  in  the  region  of  elongation  of  the  root.  First  there 
is  in  the  section  a  V-shaped  cap  of  loose  cells  which  are  constantly  being 
sloughed  off.  Just  back  of  this  tip  the  cells  are  quite  regularly  isodiametric, 
that  is,  of  equal  diameter  in  all  directions.  They  are  also  very  rich  in  pro- 
toplasm, and  have  thin  walls.  This  is  the  region  of  the  root  where  new  cells 
are  formed  by  division.  It  is  the  formative  region.  The  cells  on  the  outside 
of  this  area  are  the  older,  and  pass  over  into  the  older  parts  of  the  root  and  root 
cap.  If  we  examine  successively  the  cells  back  from  this  formative  region 
we  find  that  they  become  more  and  more  elongated  in  the  direction  of  the 
axis  of  the  root.  The  elongation  of  the  cells  in  this  older  portion  of  the  root 
explains  then  why  it  is  that  this  region  of  the  root  elongates  more  rapidly 
than  the  tip. 

252.  Growth  of  the  stem. — We  may  use  a  bean  seedling 
growing  in  the  soil.     At  the  junction  of  the  leaves  with  the  stem 
there  are  enlargements.     These  are  the  nodes,  and  the  spaces  on 
the  stem  between  successive  nodes  are  the  internodes.     We  should 
mark  off  several  of  these  internodes,  especially  the  younger  ones, 
into  sections  about  $mm  long.     Now  observe  these  at  several 
times  for  two  or  three  days,  or  more.     The  region  of  elongation 
is  greater  than  in  the  case  of  the  roots,  and  extends  back  farther 
from  the  end  of  the  stem.     In  some  young  garden  bean  plants 
the  region  of  elongation  extended  over  an  area  of  4omm  in  one 
internode.     See  also  Chapters  38,  39. 

253.  Force  exerted  by  growth. — One  of  the  marvelous  things  connected 
with  the  growth  of  plants  is  the  force  which  is  exerted  by  various  members  of 
the  plant  under  certain  conditions.     Observations  on  seedlings  as  they  are 
pushing  their  way  through  the  soil  to  the  air  often  show  us  that  considerable 
force  is.  required  to  lift  the  hard  soil  and  turn  it  to  one  side.    A  very  striking 
illustration  may  be  had  in  the  case  of  mushrooms  which  sometimes  make 
their  way  through  the  hard  and  packed  soil  of  walks  or  roads.     That  succu- 
lent and  tender  plants  should  be  capable  of  lifting  such  comparatively  heavy 
weights  seems  incredible  until  we  have  witnessed  it.     Very  striking  illustra- 
tions of  the  force  of  roots  are  seen  in  the  case  of  trees  which  grow  in  rocky 
situations,  where  rocks  of  considerable  weight  are  lifted,  or  small  rifts  in 
large  rocks  are  widened  by  the  lateral  pressure  exerted  by  the  growth  of  a 
root,  which  entered  when  it  was  small  and  wedged  its  way  in. 

254.  Zone  of  maximum  growth. — Great  variation  exists  in  the  rapidity  of 
growth  even  when  not  influenced  by  outside  conditions.      In  our  study  of  the 
elongation  of  the  root  we  found  that  the  cells  just  back  of  the  formative  region 


GRO  WTH. 


123 


elongated  slowly  at  first.  The  rapidity  of  the  elongation  of  these  cells  in« 
creases  until  it  reaches  the  maximum.  Then  the  rapidity  of  elongation  les- 
sens as  the  cells  come  to  lie  farther  from  the  tip.  The  period  of  maximum 
elongation  here  is  the  zone  of  maximum  growth  of  these  cells. 

255.  Just  as  the  cells  exhibit  a  zone  of  maximum  growth,  so  the  members  of 
the  plant  exhioit  a  similar  zone  of  maximum  growth.      In  the  case  of  leaves, 
when  they  are  young  the  rapidity  of  growth  is  comparatively  slow,  then  it 
increases,  and  finally  diminishes  in  rapidity  again.     So  it  is  with  the  stem. 
When  the  plant  is  young  the  growth  is  not  so  rapid;  as  it  approaches  middle 
age  the  rapidity  of  growth  increases;  then  it  declines  in  rapidity  at  the  close 
of  the  season. 

256.  Energy  of  growth. — Closely  related  to  the  zone  of  maximum  growth  is 
what  is  termed  the  energy  of  growth.     This  is  manifested  in  the  compara- 
tive size  of  the  members  of  a  given  plant. 
To  take  the  sunflower  for  example,  the 
lower  and  first  leaves  are  comparatively 
small.     As  the  plant  grows   larger  the 
leaves  are  larger,  and  this   increase  in 
size  of  the  leaves  increases  up  to  a  maxi- 
mum period,    when  the    size   decreases 
until  we  reach  the  small  leaves  at  the  top 
of  the  stem.  The  zone  of  maximum  growth 
of  the  leaves  corresponds  with  the  maxi- 
mum size  of  the  leaves  on  the  stem.    The 
rapidity  and  energy  of  growth  of  the  stem 
is  also  correlated  with  that  of  the  leaves, 

and  the  zone  of  maximum 
growth  is  coincident  with 
that  of  the  leaves.  It  would 
be  instructive  to  note  it 
in  the  case  of  other  plants 
and  also  in  the  case  of 
fruits. 

257.  Nutation. — During  the  growth  of  the  stem  all  of  the  cells  of  a  given 
section  of  the  stem  do  not  elongate  simultaneously.     For  example  the  cells 
at  a  given  moment  on  the  south  side  are  elongating  more  rapidly  than  the 
cells  on  the  other  side.     This  will  cause  the  stem  to  bend  slightly  to  the 
north.    In  a  few  moments  later  the  cells  on  the  west  side  are  elongating  more 
rapidly,  and  the  stem  is  turned  to  the  east ;  and  so  on,  groups  of  cells  in  suc- 
cession around  the  stem  elongate  more  rapidly  than  the  others.     This  causes 
the  stem  to  describe  a  circle  or  ellipse  about  a  central  point.     Since  the  re- 
gion of  greatest  elongation  of  the  cells  of  the  stem  is  gradually  moving  toward 
the  apex  of  the  growing  stem,  this  line  of  elongation  of  the  cells  which  is 


Lever  auxanometer  (Oels)  for  measuring 
the  stem  during  growth. 


ration  of 


124  PHYSIOLOGY, 

traveling  around  the  stem  does  so  in  a  spiral  manner.  In  the  same  way, 
while  the  end  of  the  stem  is  moving  upward  by  the  elongation  of  the  cells, 
and  at  the  same  time  is  slowly  moved  around,  the  line  which  the  end  of  the 
stem  describes  must  be  a  spiral  one.  This  movement  of  the  stem,  which  is 
common  to  all  stems,  leaves,  and  roots,  is  nutation. 

258.  The  importance  of  nutation  to  twining  stems  in  their  search  for  a 
place  of  support,  as  well  as  for  the  tendrils  on  leaves  or  stems,  will  be  seen. 
In  the  case  of  the  root  it  is  of  the  utmost  importance,  as  the  root  makes  its 
way  through  the  soil,  since  the  particles  of  soil  are  more  easily  thrust  aside. 
The  same  is  also  true  in  the  case  of  many  stems  before  they  emerge  from  the 
soil. 


CHAPTER  XIII. 

IRRITABILITY. 

259.  We  should  now  examine  the  movements  of  plant  parts 
in    response    to    the    influence    of  certain    stimuli.       By    this 
time  we  have  probably  observed  that  the  direction  which  the 
root  and  stem  take  upon  germination  of  the  seed  is  not  due  to 
the  position  in  which  the  seed  happens  to  lie.     Under  normal 
conditions  we  have  seen  that  the  root  grows  downward  and  the 
stem  upward. 

260.  Influence  of  the  earth  on  the  direction  of  growth. — 
When  the  stem  and  root  have  been  growing  in  these  directions 
for  a  short  time  let  us  place  the  seedling  in  a  horizontal  position, 
so  that  the  end  of  the  root  extends  over  an  object  of  support  in 
such  a  way  that  it  will  be  free  to  go  in  any  direction.      It  should 
be  pinned  to  a  cork  and  placed  in  a  moist  chamber.     In  the 
course  of  twelve  to  twenty-four  hours  the  root  which  was  formerly 
horizontal  has  turned  the  tip  downward  again.      If  we  should 
mark  off  millimeter  spaces  beginning  at  the  tip  of  the  root,  we 
should  find  that  the  motor  zone,  or  region  of  curvature,  lies  in 
the  same  region  as  that  of  the  elongation  of  the  root. 

Knight  found  that  the  stimulus  which  influences  the  root  to 
turn  downward  is  the  force  of  gravity.  The  reaction  of  the  root 
in  response  to  this  stimulus  is  geotropism,  a  turning  influenced 
by  the  earth.  This  term  is  applied  to  the  growth  movements  of 
plants  influenced  by  the  earth  with  regard  to  direction.  While 
the  motor  zone  lies  back  of  the  root  tip,  the  latter  receives  the 
stimulus  and  is  the  perceptive  zone.  If  the  root  tip  is  cut  off, 
the  root  is  no  longer  geotropic,  and  will  not  turn  downward 
when  placed  in  a  horizontal  position.  Growth  toward  the  earth 

125 


126 


PHYSIOLOGY. 


is  progeotropism.     The  lateral  growth  of  secondary  roots  is  dia~ 
geotropism. 

The  stem,  on  the  other  hand,  which  was  placed  in  a  horizontal 
position  has  become  again  erect.     This  turning  of  the  stem  in 


Fig.  112.  Fig.  113. 

Germinating  pea  placed  in  a  hori-  In  24  hours  gravity  has  caused  the  root  to 

zontal  position.  turn  downward. 

Figs,  iia,  113. — Progeotropism  of  the  pea  root. 

the  upward  direction  takes  place  in  the  dark  as  well  as  in  the 
light,  as  we  can  see  if  we  start  the  experiment  at  nightfall,  or 
place  the  plant  in  the  dark.  This  up- 
ward growth  of  the  stem  is  also  influ- 
enced by  the  earth,  and  therefore  is  a 
case  of  geotropism.  The  special  desig- 
nation in  the  case  of  upright  stems  is 
negative  geotropism^  or  apogeotropism,  or 
the  stems  are  said 
to  be  apogeotropic. 


Fig.  114. 

Pumpkin  seedling  showing  apogeotropism.     Seedling  at  the  left  placed  hori- 
zontally, in  24  hours  the  stem  has  become  ere'ct. 

If  we  place   a  rapidly  growing   potted   plant   in  a   horizontal 

position  by  laying  the  pot  on  its  side,   the  ends  of  the  shoots 

will   soon    turn    upward   again   when    placed    in  a   horizontal 

position.     Young  bean  plants  growing  in   a  pot  began  within 
two  hours  to  turn  the  ends  of  the  shoots  upward. 


IRRITABILITY. 


127 


Horizontal  leaves  and  shoots  can  be  shown  to  be  subject  to 
the  same  influence,  and  are  therefore  diageotropic. 

261.  Influence  of  light. — Not  only  is  light  a  very  important 
factor  for    plants    during    photosynthesis,    it  exerts  great  influ- 
ence on  plant  growth  and  movement. 

262.  Growth  in  the  absence  of  light. — Plants  grown  in  the  dark 
are  subject  to  a  number  of  changes.     The  stems  are  often  longer, 
more  slender  and 

weaker  since  they 
contain  a  larger 
amount  of  water 
in  proportion  to 
building  material 
which  the  plant 
obtains  from  car- 
bohydrates manu- 
factured in  the 
light.  On  many 
plants  the  leaves 
are  very  small 
when  grown  in  the 
dark. 

263.  Influence  of  light  on  direction  of 
growth. — While  we  are  growing  seedlings, 

the  pots  or  boxes  of  some  of  them  should  be  Fi    n6 

placed  SO  that    the  plants  will  have    a    One-  Radish  seedlings  grown  in 

.,,.,,         .         .             m,  .  the  light,  shorter,  stouter, 

Sided    illumination.       IhlS    Can   be    done   by  and  green  in  C9lor.    Growth 

,            .  retarded  by  light. 

placing  them  near  an  open  window,  in  a 

room  with  a  one-sided  illumination,  or  they  may  be  placed  in  a 
box  closed  on  all  sides  but  one  which  is  facing  the  window  or 
light.  In  12-24  hours,  or  even  in  a  much  shorter  time  in  some 
cases,  the  stems  of  the  seedlings  will  be  directed  toward  the 
source  of  light.  This  influence  exerted  by  the  rays  of  light  is 
heliotropism,  a  turning  influenced  by  the  sun  or  sunlight. 

264.  Diaheliotropism. — Horizontal    leaves    and    shoots    are 
diaheliotropic   as   well   as   diageotropic.     The   general   direction 


Fig.  115. 

Radish  seedlings  grown  in  the 

dark,  long,  slender,  not  green. 


128 


PHYSIOLOGY. 


which  leaves  assume  under  this  influence  is  that  of  placing  them 
with  the  upper  surface  perpendicular  to  the  rays  of  light  which 
fall  upon  them.  Leaves,  then,  exposed  to 
the  brightly  lighted  sky  are,  in  general, 
horizontal.  This  position  is  taken  in  direct 
response  to  the 
stimulus  of  light. 
The  leaves  of  plants 
with  a  one-sided  illu- 
mination, 
as  can  be 
seen  by 
trial,  are 
turned  with 
Fig-  "7*  their  upper 

Seedling  of  castor-oil  bean,  before  and  after 

a  one-sided  illumination.  SUrfaCCS  tO- 

ward      the 

source  of  light,  or  perpendicular  to  the  in- 
cidence of  the  light  rays.  In  this  way 
light  overcomes  for  the  time  being  the 
direction  which  growth  gives  to  the  leaves. 
The  so-called  ' '  sleep  ' '  of  plants  is  of 
course  not  sleep,  though  the  leaves  "  nod," 
or  hang  downward,  in  many  cases.  There 
—  are  many  plants  in  which  we  can  note 
this  drooping  of  the  leaves  at  nightfall,  and  in  order  to  prove 
that  it  is  not  determined  by  the  time  of  day  we  can  resort  to 
a  well-known  ex- 
periment to  induce 
this  condition  dur- 
ing the  day.  The 
plant  which  has 
been  used  to  illus- 
trate this  is  the  sun- 
flower. Some  of 


these  plants,  which 


Fig.  ii  8. 

Dark  chamber  with  opening  at  one  side  to  show  heliotropism. 
(After  Schleichert.) 


IRRITABILITY. 


I29 


were  grown  in  a  box,  when  they  were  about  $$cm  high  were 
covered  for  nearly  two  days,  so  that  the  light  was  excluded. 
At  midday  on  the  second  day  the  box  was  removed,  and  the 
leaves  on  the  covered  plants  are  well  represented  by  fig.  up,  which 
was  made  from  one  of  them.  The  leaves  of  the  other  plants 
in  the  box  which  were  not  covered  were  horizontal,  as  shown 
by  fig.  120.  Now  on  leaving  these  plants,  which  had  exhibited 


Fig.  120. 

Sunflower  plant  removed  from 
darkness,  leaves  extending  under 
influence  of  light  (diaheliotro- 
pism.) 

induced    "sleep"   move- 
ments, exposed  to  the  light 
they     gradually    assumed 
the  horizontal  position  again. 

265.  Epinasty  and  hyponasty. — During 
the  early  stages  of  growth  of  many  leaves, 
as  in  the  sunflower  plant,  the  direction  of 
growth  is  different  from  what  it  is  at  a  later 
period.  The  under  surface  of  the  young 
leaves  grows  more  rapidly  in  a  longitudinal 
direction  than  the  upper  side,  so  that  the 
leaves  are  held  upward  close  against  the 
bud  at  the  end  of  the  stem.  This  is  termed 
hyponasty,  or  the  leaves  are  said  to  be 
hyponaslic.  Later  the  growth  is  more  rapid 
on  the  upper  side  and  the  leaves  turn  downward  or  away  from  the  bud. 
This  is  termed  epinasty,  or  the  leaves  are  said  to  be  epinastic.  This  is  shown 
by  the  night  position  of  the  leaves,  or  in  the  induced  "sleep  "of  the  sun- 


Fig.  II Q. 

Sunflower  plant.  Epinastic  con- 
dition of  leaves  induced  during  the 
day  in  darkness. 


130  PHYSIOLOGY. 

flower  plant  in  the  experiment  detailed  above.  The  day  position  of  the 
leaves  on  the  other  hand,  which  is  more  or  less  horizontal,  is  induced  because 
of  their  irritability  under  the  influence  of  light,  the  inherent  downward  or 
epinastic  growth  is  overcome  for  the  time.  Then  at  nightfall  or  in  darkness, 
the  stimulus  of  light  being  removed,  the  leaves  assume  the  position  induced 
by  the  direction  of  growth. 

266.  In  the  case  of  the  cotyledons  of  some  plants  it  would  seem  that  the 
growth  was  hyponastic  even  after  they  have  opened.     The  day  position  of 


Fig.  121.  Fig.  122. 

Squash  seedling.     Position  of  cotyledons  in        Squash  seedling.     Position  of  cotyledons  in 
light.  the  dark. 

the  cotyledons  of  the  pumpkin  is  more  or  less  horizontal,  as  shown  in  fig. 
121.  At  night,  or  if  we  darken  the  plant  by  covering  with  a  tight  box,  the 
leaves  assume  the  position  shown  in  fig.  122. 

While  the  horizontal  position  is  the  general  one  which  is  assumed  by 
plants  under  the  influence  of  light,  their  position  is  dependent  to  a  certain 
extent  on  the  intensity  of  the  light  as  well  as  on  the  incidence  of  the  light 
rays.  Some  plants  are  so  strongly  heliotropic  that  they  change  their  posi- 
tions all  during  the  day. 

267.  Leaves  with  a  fixed  diurnal  position. — Leaves  of  some  plants  when 
they  are  developed  have  a  fixed  diurnal  position  and  are  not  subject  to 


IRRITABILITY. 


variation.  Such  leaves  tend  to  arrange  themselves  in  a  vertical  or  para- 
heliotropic  position,  in  which  the  surfaces  are  not  exposed  to  the  incidence 
of  light  of  the  greatest  intensity,  but  to  the  incidence  of  the  rays  of  diffused 
light.  Interesting  cases  of  the  fixed  position  of  leaves  are  found  in  the  so- 
called  compass  plants  (like  Silphium  laciniatum,  Lactuca  scariola,  etc.).  In 
these  the  horizontal  leaves  arrange  themselves  with  the  surfaces  vertical,  and 
also  pointing  north  and  south,  so  that  the  surfaces  face  east  and  west. 

268.  Importance  of  these  movements. — Not  only  are  the  leaves  placed  in 
a  position  favorable  for  the  absorption  of  the  rays  of  light  which  are  con- 
cerned in  making  carbon  available  for  food,  but  they  derive  other  forms  of 
energy  from  the  light,  as  heat,  which  is  absorbed  during  the  day.     Then 
with  the  nocturnal  position,  the  leaves  being  drooped  down  toward  the  stem, 
or  with  the  margin  toward  the  sky,  or  with  the  cotyledons  as  in  the  pump- 
kin,   castor-oil  bean,    etc.,    clasped  upward  together,    the    loss  of  heat  by 
radiation  is  less  than  it  would  be  if  the  upper  surfaces  of  the  leaves  were 
exposed  to  the  sky. 

269.  Influence  of  light  on  the  structure  of  the  leaf. — In  our  study  of  the 
structure  of  a  leaf  we  found  that  in  the  ivy  leaf  the  palisade  cells  were  on 

the  upper  surface.  This  is  the  case  with  a 
great  many  leaves,  and  is  the  normal  arrange- 
ment of  "  dorsi ventral "  leaves  which  are  dia- 
heliotropic.  Leaves  which  are  paraheliotropic 
tend  to  have  palisade  cells  on  both  surfaces. 
The  palisade  layer  of  cells  as  we  have  seen  is 
made  up  of  cells  lying  very  close  together,  and 
they  thus  prevent  rapid  evaporation.  They 
also  check  to  some  extent  the  entrance  of  the 
rays  of  light,  at  least  more  so  than  the  loose 
spongy  parenchyma  cells  do.  Leaves  developed 
in  the  shade  have  looser  palisade  and  paren- 
chyma cells.  In  the  case  of  some  plants,  if 
we  turn  over  a  very  young  leaf,  so  that  the 
under  side  will  be  uppermost,  this  side  will 
develop  the  palisade  layer.  This  shows  that 
light  has  a  great  influence  on  the  structure  of 
the  leaf. 

270.  Movement  influenced  by  contact. — In 
the  case  of  tendrils,  twining  leaves,  or  stems, 
the  irritability  to  contact  is  shown  in  a  move- 
ment  of  the  tendril,  etc.,  toward  the  object  in 
touch.  This  causes  the  tendril  or  stem  to  coil 
around  the  object  for  support.  The  stimulus  is  also  extended  down  the  part 
of  the  tendril  below  the  point  of  contact  (see  fig.  123),  and  that  part  coils 


Fig.  123- 
Coiling  tendril  of  bryony. 


132 


PHYSIOLOGY. 


up  like  a  wire  coil  spring,  thus  drawing  the  leaf  or  branch  from  which  the 
tendril  grows  closer  to  the  object  of  support.  This  coil  between  the  object 
of  support  and  the  plant  is  also  very  important  in  easing  up  the  plant  when 
subject  to  violent  gusts  of  wind  which  might  tear  the  plant  from  its  support 
were  it  not  for  the  yielding  and  springing  motion  of  this  coil. 

271.  Sensitive  plants. — These  plants  are  remarkable  for  the 
rapid  response  to  stimuli.      Mimosa  pudica  is  an  excellent  plant 
to  study  for  this  purpose. 

272.  Movement  in  response  to  stimuli. — If  we  pinch  with 
the  forceps  one  of  the  terminal  leaflets,  or  tap  it  with  a  pencil, 
the  two  end  leaflets  fold  above  the  "  vein"  of  the  pinna.      This 

is    immediately   followed 
by  the  movement  of  the 
next  pair,   and  so   on  as 
shown  in  fig.  125,  until  all 
the  leaflets  on  this  pinna 
are  closed,  then  the  stimu- 
lus  travels  down   the 
other  pinnae  in  a  simi- 
lar   manner,    and 

Fig.  1 24- 

Sensitive-plant  leaf 
in  normal  position. 


Fig.  125. 
Pinnae     fold- 
ing  up    after 
stimulus. 

soon  the  pinnae  approximate  each  other  and 

the  leaf  then  drops  downward  as  shown    in  JlS'Ia,,6'    • 

.Later    aJl    the    pinnse 

fig.  126.  The  normal  position  of  the  leaf  is  folded  and  leaf  drooped, 
shown  in  fig.  124.  If  we  jar  the  plant  by  striking  it  or  by  jarring 
the  pot  in  which  it  is  grown  all  the  leaves  quickly  collapse  into 
the  position  shown  in  fig.  126.  If  we  examine  the  leaf  now  we 
see  minute  cushions  at  the  base  of  each  leaflet,  at  the  junction  of 
the  pinnae  with  the  petiole,  and  a  larger  one  at  the  junction  of 
the  petiole  with  the  stem.  We  shall  also  note  that  the  move- 
ment resides  in  these  cushions. 


IRRITABILITY. 


133 


273.  Transmission  of  the    stimulus. — The  transmission  of 
the  stimulus  in  ;his  mimosa  from  one  part  of  the  plant  has  been 
found  to  be  along  the  cells  of  the  bast. 

274,  Cause  of  the  movement. — The  movement  is  caused  by 
a  sudden  loss  of  turgidity  on  the  part  of  the  cells  in  one  portion 
of  the  pulvinus,  as  the  cushion  is  called.      In  the  case  of  the 
large  pulvinus  at  the  base  of  the  petiole  this  loss  of  turgidity  is 
in  the  cells  of  the  lower  surface.      There  is  a  sudden  change  in 
the  condition  of  the  protoplasm  of  the  cells  here  so  that  they 
lose  a  large  part  of  their  water.     This  can  be  seen  if  with  a  sharp 
knife  we  cut  off  the  petiole  just  above  the  pulvinus  before  move- 
ment takes  place.     A  drop  of  liquid  exudes  from  the  cells  of  the 
lower  side. 

275.  Paraheliotropism  of  the  leaves  of  the  sensitive  plant. — If  the  mimosa 
plant  is  placed  in  very  intense  light  the  leaflets  will  turn  their  edges  toward 
the  incidence  of  the  rays  of  light.  This  is  also  true  of  other  plants  in 
intense  light,  and  is  paraheliotropism.  Transpiration  is  thus  lessened,  and 
chlorophyll  is  protected  from  too  intense  light. 

We  thus  see  that  variations  in  the  intensity  of  light  have  an  important 
influence  in  modifying  movements.  Variations  in  temperature  also  exert 

a  considerable  influence,  rapid 
elevation  of  temperature  causing 
certain  flowers  to  open,  and 
falling  temperature  causing 
them  to  close. 

276.  Sensitiveness  of  insec- 
tivorous plants.  — -  The  Venus 
fly-trap  (Dionaea  muscipula)and 
the  sundew  (drosera)  are  in- 
teresting examples  of  sensitive 
plants,  since  the  leaves  close  in 
response  to  the  stimulus  from 
insects. 


Fig.  126. 
Leaf    of  Venus 


trap    (Dionsea     musci- 

g 
toothed 


ap 

pula),  showing  winged 
petiole      and 
lobes. 


Fig  127. 

fly-  Leaf  of  Drosera  ro- 
tundifolia,  some  of  the 
glandular  hairs  folding 
inward  as  a  result  of  a 
stimulus. 


277.    Hydrotropism — 

Roots  are  sensitive  to  mois- 
ture. They  will  turn  toward  moisture.  This  is  of  the  greatest 
importance  for  the  well-being  of  the  plant,  since  the  roots  will  seek 
those  places  in  the  soil  where  suitable  moisture  is  present.  On 


134  PHYSIOLOGY. 

the  other  hand,  if  the  soil  is  too  wet  there  is  a  tendency  for  the 
roots  to  grow  away  from  the  soil  which  is  saturated  with  water. 
In  such  cases  roots  are  often  seen  growing  upon  the  surface  of 
the  soil  so  that  they  may  obtain  oxygen,  which  is  important  for 
the  root  in  the  processes  of  absorption  and  growth.  Plants  then 
may  be  injured  by  an  excess  of  water  as  well  as  by  a  lack  of 
water  in  the  soil. 

278  Temperature.  —  In  the  experiments  on  germination  thus  far  made 
it  has  probably  been  noted  that  the  temperature  has  much  to  do  with  the 
length  of  time  taken  for  seeds  to  germinate.  It  also  influences  the 
rate  of  growth.  The  effect  of  different  temperatures  on  the  germination  of 
seed  can  be  very  well  noted  by  attempting  to  germinate  some  in  rooms  at 
various  temperatures.  It  will  be  found,  other  conditions  being  equal,  that 
in  a  moderately  warm  room,  or  even  in  one  quite  warm,  25-30  degrees  cen- 
tigrade, germination  and  growth  goes  on  more  rapidly  than  in  a  cool  room, 
and  here  more  rapidly  than  in  one  which  is  decidedly  cold.  In  the  case  of 
most  plants  in  temperate  climates,  growth  may  go  on  at  a  temperature  but 
little  above  freezing,  but  few  will  thrive  at  this  temperature. 

279.  If  we  place  dry  peas  or  beans  in  a  temperature  of  about  70°  C.  for  15 
minutes  they  will  not  be  killed,  but  if  they  have  been  thoroughly  soaked  in 
water  and  then  placed  at  this  temperature  they  will  be  killed,  or  even  at  a 
somewhat  lower  temperature.     The  same  seeds  in  the  dry  condition  will 
withstand  a  temperature  of  10°  C.  below,  but  if  they  are  first  soaked  in  water 
this  low  temperature  will  kill  them. 

280.  In  order  to  see  the  effect  of  freezing  we  may  thoroughly  freeze  a  sec- 
tion of  a  beet  root,  and  after  thawing  it  out  place  it  in  water.     The  water  is 
colored  by  the  cell-sap  which  escapes  from  the  cells,  just  as  we  have  seen  it 
does  as  a  result  of  a  high  temperature,  while  a  section  of  an  unfrozen  beet 
placed  in  water  will  not  color  it  if  it  was  previously  washed. 

If  the  slice  of  the  beet  is  placed  at  about  —  6°  C.  in  a  shallow  glass  vessel, 
and  covered,  ice  will  be  formed  over  the  surface.  If  we  examine  it  with  the 
microscope  ice  crystals  will  be  seen  formed  on  the  outside,  and  these  will 
not  be  colored.  The  water  for  the  formation  of  the  crystals  came  from  the 
cell-sap,  but  the  concentrated  solutions  in  the  sap  were  not  withdrawn  by 
the  freezing  over  the  surface. 

281.  If  too  much  water  is  not  withdrawn  from  the  cells  of  many  plants  in 
freezing,  and  they  are  thawed  out  slowly,  the  water  which  was  withdrawn 
from  the  cells  will  be  absorbed  again  and  the  plant  will  not  be  killed.     But 
if  the  plant  is  thawed  out  quickly  the  water  will  not  be  absorbed,  but  will 
remain  on  the  surface  and  evaporate.     Some  will  also  remain  in  the  inter- 
cellular spaces,  and  the  plant  will  die.    Some  plants,  however,  no  matter  how 


IRRITA  BILIT  Y.  135 

slowly  they  are  thawed  out,  are  killed  after  freezing,  as  the  leaves  of  the 
pumpkin,  dahlia,  or  the  tubers  of  the  potato. 

282.  It  has  been  found  that  as  a  general  rule  when  plants,  or  plant  parts, 
contain  little  moisture  they  will  withstand  quite  high  degrees  of  tempera- 
ture, as  well  as  quite  low  degrees,  but  when  the  parts  are  filled  with  sap  or 
water  they  are  much  more  easily  killed.  For  this  reason  dry  seeds  and  the 
winter  buds  of  trees,  and  other  plants,  because  they  contain  but  little  water, 
are  better  able  to  resist  the  cold  of  winters.  But  when  growth  begins  in  the 
spring,  and  the  tissues  of  these  same  parts  become  turgid  and  filled  with 
water,  they  are  quite  easily  killed  by  frosts.  It  should  be  borne  in  mind, 
however,  that  there  is  great  individual  variation  in  plants  in  this  respect, 
some  being  more  susceptible  to  cold  than  others.  There  is  also  great  varia- 
tion in  plants  as  to  their  resistance  to  the  cold  of  winters,  and  of  arctic 
climates,  the  plants  of  the  latter  regions  being  able  to  resist  very  low  tem- 
peratures. We  have  examples  also  in  the  arctic  plants,  and  those  which 
grow  in  arctic  climates  on  high  mountains,  of  plants  which  are  able  to  carry 
on  all  the  life  functions  at  temperatures  but  little  above  freezing. 

For  further  discussion  as  to  relation  of  plants  to  temperature,  see  Chap 
ters  46,  48,  40,  and  53. 


PART  II. 

MORPHOLOGY    AND    LIFE     HISTORY    OF    REPRE- 
SENTATIVE   PLANTS. 

CHAPTER  XIV. 

SPIROGYRA. 

283.  In  our  study  of  protoplasm  and  some  of  the  processes  of 
plant  life  we  became  acquainted  with  the  general  appearance  of 
the  plant  spirogyra.     It  is  now  a  familiar  object  to  us.     And  in 
taking  up  the  study  of  representative  plants  of  the  different 
groups,  we  shall  find  that  in  knowing  some  of  these  lower  plants 
the  difficulties  of  understanding  methods  of  reproduction  and 
relationship  are  not  so  great  as  they  would  be  if  we  were  entire- 
ly ignorant  of  any  members  of  the  lower  groups. 

284.  Form  of  spirogyra. — We  have  found   that  the  plant 
spirogyra   consists    of  simple    threads,    with    cylindrical    cells 
attached  end  to  end.     We  have  also  noted  that  each  cell  of  the 
thread  is  exactly  alike,  with  the  exception  of  certain  "  hold- 
fasts "  on  some  of  the  species.      If  we  should  examine  threads  in 
different  stages  of  growth  we  should  find  that  each  cell  is  capable 
of  growth  and  division,  just  as  it  is  capable  of  performing  all  the 
functions  of  nutrition  and  assimilation.      The  cells  of  spirogyra 
then  multiply  by  division.      Not  simply  the  cells  at  the  ends  of 
the  threads  but  any  and  all  of  the  cells  divide  as  they  grow,  and 
in  this  way  the  threads  increase  in  length. 

285.  Multiplication  of  the  threads. — In  studying  living  material  of  this 
plant  we  have  probably  noted  that  the  threads  often  become  broken  by  two  of 
the  adjacent  cells  of  a  thread  becoming  separated.  This  may  be  and  is  accom- 

136 


SPIROG  YRA. 


'37 


plished  in  many  cases  without  any  injury  to  the  cells.  In  this  manner  the 
threads  or  plants  of  spirogyra,  if  we  choose  to  call  a  thread  a 
plant,  multiply,  or  increase.  In  this  breaking  of  a  thread  the 
cell  wall  which  separates  any  two  cells  splits.  If  we  should 
examine  several  species  of  spirogyra  we  would  probably  find 
threads  which  present  two  types  as  regards  the  character  of 
the  walls  at  the  ends  of  the  cells.  In  fig.  128  we  see  that  the 
ends  are  plain,  that  is,  the  cross  walls  are  all  straight.  But 
in  some  other  species  the  inner  wall  of  the  cells  presents  a 
peculiar  appearance.  This  inner  wall  at  the  end  of  the 
cell  is  at  first  straight  across.  But  it  soon  becomes  folded 
back  into  the  interior  of  its  cell,  just  as  the  end  of  an 
empty  glovf  finger  may  be  pushed  in.  Then  the  infolded 
end  is  pushed  partly  out  again,  so  that  a  peculiar  figure  is 
the  result. 

286.  How  some  ol  the  threads  break. — In  the  separation 
of  the  cells  of  a  thread  this  peculiarity  is  often  of  advan- 
tage to  the  plant.  The  cell -sap  within  the  protoplasmic 
membrane  absorbs  water  and  the  pressure  pushes  on  the 
ends  of  the  infolded  cell  walls.  The  inner  wall  being  so 
much  longer  than  the  outer  wall,  a  pull  is  exerted  on  the 
latter  at  the  junction  of  the  cells.  Being  weaker  at  this 
point  the  outer  wall  is  ruptured.  The  turgidity  of  the  two 
cells  causes  these  infolded  inner  walls  to  push  out  suddenly 
as  the  outer  wall  is  ruptured,  and  the  thread  is  snapped 
apart  as  quickly  as  a  pipe-stem  may  be  broken. 

287.  Conjugation  of  spirogyra. — Under  cer- 
tain conditions,  when  vegetative  growth  and 
multiplication  cease,  a  process  of  reproduction 
takes  place  which  is  of  a  kind  termed  sexual  repro- 
duction. If  we  select  mats  of  spirogyra  which 
have  lost  their  deep  green  color,  we  are  likely  to 
find  different  stages  of  this  sexual  process,  which 
in  the  case  of  spirogyra  and  related  plants  is  called 
conjugation.  A  few  threads  of  such  a  mat  we 
should  examine  with  the  microscope.  If  the 
material  is  in  the  right  condition  we  see  in  certain 
of  the  cells  an  oval  or  elliptical  body.  If  we 
note  carefully  the  cells  in  which  these  oval  bodies 
are  situated,  there  will  be  seen  a  tube  at  one  side  which  con- 


Fig.  128. 

Thread  of  spiro- 
gyra, showing  lone 
cells,  chlorophyll 
band,  nucleus, 
strands  of  proto- 
plasm, and  the 
granular  wall  layer 
of  protoplasm. 


138 


MORPHOLOGY. 


nects  with  an  empty  cell  of  a  thread  which  lies  near  as  shown  in 

jjg.  1 29.  If  we  search  through  the  material  we  may  see  other  threads 

connected  in  this  ladder  fashion,  in  which 

the  contents  of  the  cells  are  in  various  stages 

of  collapse  from  what  we  have  seen  in  the 

growing  cell.     In  some  the  protoplasm  and 

chlorophyll  band  have  moved  but  little  from 

the  wall ;   in  others  it  forms  a  mass  near  the 

center  of  the  cell,  and  again  in  others  we 

will  see  that  the  contents  of  the  cell  of  one 

of  the  threads  has  moved  partly  through  the 

tube  into  the  cell  of  the  thread  with  which  it 

is  connected. 

289.  This  suggests  to  us  that  the 
oval  bodies  found  in  the  cells  of  one 
thread  of  the  ladder,  while  the  cells 
of  the  other  thread  were  empty,  are 
formed  by  the  union  of  the  contents 
of  the  two  cells.     In  fact  that  is  what 
does  take  place.     This  kind  of  union 
of  the  contents  of  two  similar  or  nearly 
similar  cells  is  conjugation.     The  oval 
bodies  which  are  the  result  of  this 
conjugation  are  zygotes,  or  zygospores. 
When  we  are  examining  living  ma- 
terial of  spirogyra  in  this  stage  it  is 
possible  to  watch  this  process  of  con- 
jugation. Fig.  130  represents  the  differ- 
ent stages  of  conjugation  of  spirogyra. 

290.  How  the  threads  conjugate,  or  join. — The  cells  of  two 
threads  lying  parallel  put  out  short  processes.     The  tubes  from 
two  opposite  cells  meet  and  join.     The  walls  separating  the  con- 
tents of  the  two  tubes  dissolve  so  that  there  is  an  open  communi- 
cation between  the  two  cells.     The  content  of  each  one  of  these 
cells  which  take  part  in  the  conjugation  is  a  gamete.     The  one 
which  passes  through  the  tube  to  the  receiving  cell  is  the  supply- 


Fig.  129. 
Zygospores  of  spirogyra. 


SP1ROG  YJ?A. 

ing  gamete,  while  that  of  the  receiving  cell  is  the  receiving 
gamete. 

291.  How  the  protoplasm  moves  from  one  cell  to  another. — Before  any 
movement  of  the  protoplasm  of  the  supplying  cell  takes  place  we  can  see 


Fig.  130. 

Conjugation  in  spirogyra ;  from  left  to  right  beginning  in  the  upper  row  is  shown  the 
gradual  passage  of  the  protoplasm  from  the  supplying  gamete  to  the  receiving  gamete. 

that  there  is  great  activity  in  its  protoplasm.  Rounded  vacuoles  appear 
which  increase  in  size,  are  filled  with  a  watery  fluid,  and  swell  up  like  a 
vesicle,  and  then  suddenly  contract  and  disappear.  As  the  vacuole  disap- 
pears it  causes  a  sudden  movement  or  contraction  of  the  protoplasm  around 
it  to  take  its  place.  Simultaneously  with  the  disappearance  of  the  vacuole 
the  membrane  of  the  protoplasm  is  separated  from  a  part  of  the  wall.  This 
is  probably  brought  about  by  a  sudden  loss  of  some  of  the  water  in  the  cell- 
sap.  These  activities  go  on,  and  the  protoplasmic  membrane  continues  to 
slip  away  from  the  wall.  Every  now  and  then  there  is  a  movement  by 
which  the  protoplasm  is  moved  a  short  distance.  It  is  moved  toward  the 
tube  and  finally  a  portion  of  it  with  one  end  of  the  chlorophyll  band  begins 
to  move  into  the  tube.  About  this  time  the  vacuoles  can  be  seen  in  an 
active  condition  in  the  receptive  cell.  At  short  intervals  movement  con- 


140 


MORPHOLOG  Y. 


tinues  until  the  content  of  the  supplying  cell  has  passed  over  into  that  of  the 
receptive  cell.  The  protoplasm  of  this  one  is  now  slipping  away  from  the 
cell  wall,  until  finally  the  two  masses  round  up  into  the  one  zygospore. 

292.  The  zygospore. — This  zygospore  now  acquires  a  thick  wall  which 
eventually  becomes  brown  in  color.     The  chlorophyll  color  fades  out,  and  a 
large  part  of  the  protoplasm  passes  into  an  oily  substance  which  makes  it 
more  resistant  to  conditions  which  would  be  fatal  to  the  vegetative  threads. 
The  zygospores  are  capable  therefore  of  enduring  extremes  of  cold  and  dry- 
ness  which  would  destroy  the  threads.     They  pass  through  a   "resting" 
period,  in  which  the  water  in  the  pond  may  be  frozen,  or  dried,  and  with  the 
oncoming  of  favorable  conditions  for  growth  in  the  spring  or  in  the  autumn 
they  germinate  and  produce  the  green  thread  again. 

293.  Life  cycle. — The  growth  of  the  spirogyra  thread,  the  conjugation  of 
the  gametes  and  formation  of  the  zygospore,  and  the  growth  of  the  thread 
from  the  zygospore  again,  makes  what  is  called  a  complete  life  cycle. 

294.  Fertilization. — While  conjugation  results  in  the  fusion  of  the   two 
masses  of  protoplasm,  fertilization  is  accomplished  when  the  nuclei  of  the 
two  cells  come  together  in  the  zygospore  and  fuse  into  a  single  nucleus.    The 


Fig.  131. 


Fertilization  in  spirogyra  ;  shows  different  stages  of 
•gospore  at  right.     (After  Overton.) 


fusion  of  the  two  nuclei,  with  mature 


xygospo 


different  stages  in  the  fusion  of  the  two  nuclei  of  a  recently  formed  zygospore 
are  shown  in  figure  131. 

In  the  conjugation  of  the  two  cells,  the  chlorophyll  band  of  the  supplying 
cell  is  said  to  degenerate,  so  that  in  the  new  plant  the  number  of  chlorophyll 
bands  in  a  cell  is  not  increased  by  the  union  of  the  two  cells. 

295.  Simplicity  of  the  process. — In  spirogyra  any  cell  of  the  thread 
may  form  a  gamete  (excepting  the  holdfasts  of  some  species).  Since  all  of 
the  cells  of  a  thread  are  practically  alike,  there  is  no  structural  difference 
between  a  vegetative  cell  and  a  cell  about  to  conjugate.  The  difference  is  a 
physiological  one.  All  the  cells  are  capable  of  conjugation  if  the  physiolog- 
ical conditions  are  present.  All  the  cells  therefore  are  potential  gametes. 
(Strictly  speaking  the  wall  of  the  cell  is  the  garnet  angium,  while  the  content 
forms  the  gamete.) 

While  there  is  sometimes  a  slight  difference  in  size  between  the  conjugal- 


SPIROGYRA. 


141 


ing  cells,  and  the  supplying  cell  may  be  the  smaller,  this  is  not  general.  We 
say,  therefore,  that  there  is  no  differentiation  among  the  gametes,  so  that 
usually  before  the  protoplasm  begins  to  move  one  cannot  say  which  is  to  be 
the  supplying  and  which  the  receiving  gamete. 

296.  Position  of  the  plant  spirogyra. — From  our  study  then  we  see  that 
there   is   practically  no  differentiation  among  the  vegetative  cells,    except 
where  holdfasts  grow  out  from  some  of  the  cells  for  support.     They  are  all 
alike   in   form,    in  capacity  for   growth,   division,  or   multiplication  of  the 
threads.     Each  cell  is  practically  an  independent  plant.     There  is  no  differ-- 
entiation  between  vegetative  cell  and  conjugating  cell.     All  the  cells  are 
potential  gametes.     Finally  there  is  no  structural  differentiation  between  the 
gametes.     This  indicates  then  a  simple  condition  of  things,  a  low  grade  of 
organization. 

297.  The  alga  spirogyra  is  one  of  the  representatives  of  the  lower  algae 
belonging  to  the  group  called  Conjugate.     Zygnema  with  star-shaped  chloro- 
plasts,  mougeotia  with  straight  or  sometimes  twisted  chlorophyll  bands,  be- 
long to  the  same  group.     In  the  latter  genus  only  a  portion  of  the  protoplasm 
of  each  cell  unites  to  form  the  zygospore,  which  is  located  in  the  tube  between 
the  cells. 


Fig.  133. 
Micrasterias. 


Fig.  134- 
Xanthidium, 


Fig.  132. 
Closterium. 


Fig.  i37. 
Cosmarium. 


298.  The  desmids  also  belong  to  the  same  group.  The  desmids  usually  live 
as  separate  cells.  Many  of  them  are  beautiful  in  form.  They  grow  entangled 
among  other  algae,  or  on  the  surface  of  aquatic  plants,  or  on  wet  soil.  Sev- 
eral genera  are  illustrated  in  figures  132-137. 


CHAPTER  XV. 


VAUCHERIA. 

299.  The  plant  vaucheria  we  remember  from  our  study  in 
an  earlier  chapter.  It  usually  occurs  in  dense  mats  floating 
on  the  water  or  lying  on  damp  soil.  The  texture  and  feeling  of 
these  mats  remind  one  of  "felt," 
and  the  species  are  sometimes  called 
the  "  green  felts."  x  The  branched 
threads  are  continuous,  that  is  there 
are  no  cross  walls  in  the  vegetative 
threads.  This  plant  multiplies  it- 
self in  several  ways  which  would 
be  too  tedious  to  detail  here.  But 
when  fresh  bright  green  mats  can  be 
obtained  they  should  be  placed  in 
a  large  vessel  of  water  and  set  in 
a  cool  place.  Only  a  small  amount 
of  the  alga  should  be  placed  in  a 
vessel,  since  decay 
will  set  in  more 
rapidly  with  a  large 
quantity.  For 
several  days  one 
should  look  for 

small  green  bodies  which  may  be  floating  at  the  side  of  the  vessel 
next  the  lighted  window. 

300.  Zoogonidia  of  vaucheria. — If  these  minute  floating  green  bodies  are 
found,  a  small  drop  of  water  containing  them  should  be  mounted  for  exami- 

142 


Fig.i38. 
Portion  of  branched  thread  o.  vaucheria 


VAUCHERIA.  143 

nation.  If  they  are  rounded,  with  slender  hair-like  appendages  over  the 
surface,  which  vibrate  and  cause  motion,  they  very  likely  are  one  of  the 
kinds  of  reproductive  bodies  of  vaucheria.  The  hair-like  appendages  are 
cilia,  and  they  occur  in  pairs,  several  of  them  distributed  over  the  surface. 
These  rounded  bodies  are  gonidia,  and  because  they  are  motile  they  are 
called  zoogonidia. 

By  examining  some  of  the  threads  in  the  vessel  where  they  occurred  we 
may  have  perhaps  an  opportunity  to  see  how  they  are  produced.  Short 
branches  are  formed  on  the  threads,  and  the  contents  are  separated  from 
those  of  the  main  thread  by  a  septum.  The  protoplasm  and  other  contents  of 
this  branch  separate  from  the  wall,  round  up  into  a  mass,  and  escape  through 
an  opening  which  is  formed  in  the  end.  Here  they  swim  around  in  the 
water  for  a  time,  then  come  to  rest,  and  germinate  by  growing  out  into  a 
tube  which  forms  another  vaucheria  plant.  It  will  be  observed  that  this 
kind  of  reproduction  is  not  the  result  of  the  union  of  two  different  parts  of 
the  plant.  It  thus  differs  from  that  which  is  termed  sexual  reproduction.  A 
small  part  of  the  plant  simply  becomes  separated  from  it  as  a  special  body, 
and  then  grows  into  a  new  plant,  a  sort  of  multiplication.  This  kind  of  re- 
production has  been  termed  asexual  reproduction. 

301.  Sexual  reproduction  in  vaucheria. — The  organs  which  are  concerned 
in  sexual  reproduction  in  vaucheria  are  very  readily  obtained  for  study  if 
one  collects  the  material  at  the  right  season.  They  are  found  quite  readily 
during  the  spring  and  autumn,  and  may  be  preserved  in  formalin  for  study 
at  any  season,  if  the  material  cannot  be  collected  fresh  at  the  time  it  is 
desired  for  study.  Fine  material  for  study  often  occurs  on  the  soil  of  pots  in 

greenhouses  during  the  winter. 
While  the  zoogonidia  are  more 
apt  to  be  found  in  material 
which  is  quite  green  and  fresh- 
ly growing,  the  sexual  organs 
are  usually  more  abundant 
when  the  threads  appear  some- 
what yellowish,  or  yellow 
green. 

302.  Vaucheria  sessi- 
Us;  the  sessile  vauche- 

Young  antheridium  and  oogonium  of  Vaucheria  ses-  -,  ,   .  .  , 

silis,  before  separation  from   contents  of  thread  by  a  Iia.— - 

sexual  organs  are  sessile, 

that  is  they  are  not  borne  on  a  stalk  as  in  some  other  species. 
The  sexual  organs  usually  occur  several  in  a  group.  Fig.  139 
represents  a  portion  of  a  fruiting  plant. 


144 


MORPHOLOGY. 


303.  Sexual    organs   of   vaucheria.      Anther idium. — The 

antheridia  are  short,  slender,  curved  branches  from  a  main 
thread.  A  septum  is  formed  which  separates  an  end  portion 
from  the  stalk.  This  end  cell  is  the  antheridium.  Frequently  it 
is  collapsed  or  empty  as  shown  in  fig.  140.  The  protoplasm  in 


Fig.  140. 
Vaucheria  sessilis,  one  antheridium  between  two  oogonia. 

the  antheridium  forms  numerous  small  oval  bodies  each  with  two 
slender  lashes,  the  cilia.  When  these  are  formed  the  antherid- 
ium opens  at  the  end  and  they  escape.  It  is  after  the  escape 
of  these  spermatozoids  that  the  antheridium  is  collapsed.  Each 
spermatozoid  is  a  male  gamete. 

304.   Oogonium.  —  The  oogonia  are  short  branches  also,  but 
they    become     large    and  ,1 

somewhat     oval.        The  f  \ 

septum  which  separates  the 
protoplasm  from  that  of 
the  main  thread  is  as  we 
see  near  the  junction  of 
the  branch  with  the  main 

thread.         The     OOgOnium, 

UQ  shown     in   tVip    ficnirp     I'Q 
tne    ngure,   IS 

usually  turned  somewhat 
to  one  side.  When  mature  the  pointed  end  opens  and  a  bit  of  the 
protoplasm  escapes.  Th'e  remaining  protoplasm  forms  the  large 
rounded  egg  cell  which  fills  the  wall  of  the  oogonium.  In  some 
of  the  oogonia  which  we  examine  this  egg  is  surrounded  by  a 
thick  brown  wall,  with  starchy  and  oily  contents.  This  is  the 


Vaucheria  sessilis  ogonium  opening  and  emit- 
ting  a  bit  of  protoplasm;  spermatozoids;  sperma- 
tQz*  ids  enteri£g  00£onium.  *%&&  pringsheim  and 

Goebe1-) 


VA  UCHERIA. 


145 


fertilized  egg  (sometimes  called  here  the  oospore).    It  is  freed 
from  the  oogonium  by  the  disintegration  of  the  latter,  sinks  into 


Fig.  142. 

Fertilization  in  vaucheria.    w«,  male  nucleus  ;  fn,  female  nucleus.    Male  nucleus  entering 
the  egg  and  approaching  the  female  nucleus.     (After  Oltmans.) 

the  mud,  and  remains  here  until  the  following  autumn  or  spring, 
when  it  grows  directly  into  a  new  plant. 

305.   Fertilization. — Fertilization    is    accomplished   by  the 
spermatozoids  swimming  in  at  the  open  end  of  the  oogonium, 


Fig.  143. 

Fertilization  of  vaucheria.   fn,  female  nucleus;  tun,  male  nucleus.     The  different  figures 
show  various  stages  in  the  fusion  of  the  nuclei. 

when  one  of  them  makes  its  way  down  into  the  egg  and  fuses 
with  the  nucleus  of  the  egg. 

306.  The  twin  vaucheria  (V.  geminata). — Another  species  of  vaucheria 
\s  the  twin  vaucheria.     This  is  also  a  common  one,  and  may  be  used  for 
>tudy  instead  of  the  sessile  vaucheria  if  the  latter  cannot  be  obtained.     The 
sexual  organs  are  borne  at  the  end  of  a  club-shaped  branch.     There  are 
usually  two  oogonia,  and  one  antheridium  between  them  which  terminates 
the  branch.     In  a  closely  related  species,  instead  of  the  two  oogonia  there  is 
a  whorl  of  them  with  the  antheridium  in  the  center. 

307.  Vaucheria  compared  with  spirogyra. — In  vaucheria  we  have  a  plant 
rhich  is  very  interesting  to  compare  with  spirogyra  in  several  respects. 


146 


MOKPHOLOG  Y. 


Growth  takes  place,  not  in  all  parts  of  the  thread,  but  is  localized  at  the  ends 
of  the  thread  and  its  branches.  This  represents  a  distinct  advance  on  such 
a  plant  as  spirogyra.  Again,  only  specialized  parts  of  the  plant  in  vaucheria 
form  the  sexual  organs.  These  are  short  branches.  Farther  there  is  a  great 
difference  in  the  size  of  the  two  organs,  and  especially  in  the  size  of  the 
gametes,  the  supplying  gametes  (spermatozoids)  being  very  minute, 
while  the  receptive  gamete  is  large  and  contains  all  the  nutriment  for  the 
fertilized  egg.  In  spirogyra,  on  the  other  hand,  there  is  usually  no  differ- 
ence in  size  of  the  gametes,  as  we  have  seen,  and  each  contributes  equally  in 
the  matter  of  nutriment  for  the  fertilized  egg.  Vaucheria,  therefore,  rep- 
resents a  distinct  advance,  not  only  in  the  vegetative  condition  of  the  plant, 
but  in  the  specialization  of  the  sexual  organs.  Vaucheria,  with  other  related 
algae,  belongs  to  a  group  known  as  the  Siphonece,  so  called  because  the  plants 
are  tube-like  or  siphon-\\\&. 

308.    Botrydium  granulatum.  —  An    example   of    orte   of   the   simpler 

members  of  the  Siphoneae  is 
Botrydium  granulatum.  It  is 
found  sometimes  in  abundance 
on  wet  ground  which  is  colored 
green  or  red  by  its  presence, 
according  to  the  stage  of  de- 
velopment. The  plant  body  is 
long  pear-shaped,  the  smaller 
end  attached  to  the  ground  by 
slender  branched  rhizoids  (Fig. 
143).  The  protoplasm  contains 
many  nuclei  and  lines  the  inside 
of  the  wall.  When  multiplication 
takes  place  large  numbers  of 
small  zoospores  with  one  cilium 
each  are  formed  in  the  proto- 
plasm, and  escape  at  free  end. 
Reproduction  takes  place  by 
two-ciliated  gametes,  which  fuse 
in  pairs  to  form  zygospores.  In 
dry  seasons  the  protoplasm  in 
the  pear-shaped  plant  passes 
down  into  the  rhizoids  and 
forms  small  rounded  planospores. 
All  the  stages  of  development  are  too  complicated  to  describe  here. 


Fig.  i43a. 

Botrydium  granulatum.  A,  the  whole 
plant;  B,  swarm  spore;  C,  planogametes ;  a, 
a  single  gamete;  b-e,  two  gametes  in  process 
of  fusion;  /,  zygote. 


CHAPTER  XVI. 

CEDOGONIUM. 

309.  (Edogonium  is  also  an  alga.     The  plant  is  sometimes 
associated  with  spirogyra,  and  occurs  in  similar  situations.      Our 
attention  was  called  to  it  in  the  study  of  chlorophyll  bodies. 
These  we  recollect  are,  in  this  plant,  small  oval  disks,  and  thus 
differ  from  those  in  spirogyra. 

310.  Form    of   cedogonium. — Like    spirogyra,    oedogonium 
forms   simple    threads   which  are  made  up  of  cylindrical  cells 
placed  end  to  end.      But  the  plant  is  very  different  from  any 
member  of  the  group  to  which  spirogyra  belongs.     In  the  first 
place  each  cell  is  not  the  equivalent  of  an  individual  plant  as  in 
spirogyra.      Growth  is  localized  or  confined  to  certain  cells  of 
the  thread  which  divide  at  one  end  in  such  a  way  as  to  leave  a 
peculiar  overlapping  of  the  cell  walls  in  the  form  of  a  series  of 
shallow  caps  or  vessels  (fig.  144),  and  this  is  one  of  the  character- 
istics of  this  genus.     Other  differences  we  find  in  the  manner  of 
reproduction. 

311.  Fruiting  stage  of  oadogonium. — Material  in  the  fruiting 
stage  is  quite  easily  obtainable,  and  may  be  preserved  for  study 
in  formalin  if  there  is  any  doubt  about  obtaining  it  at  the  time 
we  need  it  for  study.      This  condition  of  the  plant  is  easily  de- 
tected because  of  the  swollen  condition  of  some  of  the  cells,  or 
by  the  presence  of  brown  bodies  with  a  thick  wall  in  some  of  the 
cells, 

312.  Sexual  organs  of  oedogonium.     Oogonium  and  egg.— 
The  enlarged  cell  is  the  oogonium,  the  wall  of  the  cell  being  the 
walloftheoogonium.   (See  tig.  145.)  The  protoplasm  inside,  before 

H7 


148 


MORPHOLOG  Y. 


fertilization,  is  the  egg  cell.  In  those  cases  where  the  brown  body 
with  a  thick  wall  is  present  fertilization  has  taken  place,  and  this 
body  is  the  fertilized  egg,  oroospore.  It  contains 
large  quantities  of  an  oily  substance,  and,  like 


Fig.  144. 

Portion  o  f 
thread  of  oedo- 
gonium,  show- 
ing chlorophyll 
grains,  and  pe- 
culiar cap  cell 
walls. 


Fig.  145. 

CEdogonium   undulatum,  with  oogonia  and  dwarf  males; 
the  upper  oogonium  at  the  right  has  a  mature  oospore. 


the  fertilized  egg  of  spirogyra  and  vaucheria,  is  able  to  with- 
stand greater  changes  in  temperature  than  the  vegetative  stage, 
and  can  endure  drying  and  freezing  for  some  time  without 
injury. 

In  the  oogonium  wall  there  can  frequently  be  seen  a  rift  near 
the  middle  of  one  side,  or  near  the  upper  end.     This  is  the 


(EDOGONIUM. 


149 


opening  through  which  the  spermatozoid  entered  to  fecundate 
the  egg. 

313.  Dwarf  male  plants. — In  some  species  there  will  also  be 
seen  peculiar  club-shaped  dwarf  plants  attached  to  the  side  of  the 
oogonium,  or  near  it,  and  in  many  cases  the  end  of  this  dwarf 
plant  has  an  open  lid  on  the  end. 

314.  Antheridium. — The  end  cell  of  the  dwarf  male  in  such 
species  is  the  antheridium.      In  other  species  the  spermatozoids 
are  developed  in  different  cells  (antheridia)  of  the  same  thread 
which  bears  the  oogonium,  or  on  a  different  thread. 

315.  Zoospore  stage  of  cedogonium. — The  egg  after  a  period  of  rest  starts 
into  active  life  again.     In  doing  so  it  does  not  develop  the  thread-like  plant 
directly  as  in  the  case  of  vaucheria  and  spirogyra.     It  first  divides  into  four 
zoospores  which  are  exactly  like  the  zoogonidia  in  form.     (See  fig.  152.) 
These  germinate  and  develop  the  thread  form  again.     This  is  a  quite  re- 
markable peculiarity  of  oeclogonium  when  compared  with  either  vaucheria 
or  spirogyra.      It  is  the  introduction  of  an  intermediate  stage  between  the 
fertilized  egg  and  that  form  of  the  plant  which  bears  the  sexual  organs,  and 
should  be  kept  well  in  mind. 

316.  Asexual  reproduction. — Material  for  the  study  of  this  stage  of  oedo- 
gonium  is  not  readily  obtainable  just  when  we  wish  it  for  study.     But  fresh 
plants  brought  in  and  placed  in  a 

quantity  of  fresh  water  may  yield 
suitable  material,  and  it  should  be 
examined  at  intervals  for  several 
days.  This  kind  of  reproduction 
takes  place  by  the  formation  of 
zoogonidia.  The  entire  contents 
of  a  cell  round  off  into  an  oval 


Fig.  146. 

Zoogonidia  of  oedogonium  escaping. 
At  the  right  one  is  germinating  and 
forming  the  holdfasts,  by  means  of  which 
these  algae  attach  themselves  to  objects 
for  support.  (After  Pringsheim.) 


body,  the  wall  of  the  cell  breaks, 

and  the  zoogonidium  escapes.     It 

has   a   clear   space  at  the  small 

end,  and  around  this  clear  space 

is  a  row  or  crown  of  cilia  as  shown  in  fig.  146.    By  the  vibration  of  these  cilia 

the  zoogonidium  swims  around  for  a  time,  then  settles  down  on  some  object  of 

support,  and  several  slender  holdfasts  grow  out  in  the  form  of  short  rhizoids 

which  attach  the  young  plant. 

317.  Sexual  reproduction.  Antheridia. — The  antheridia  are  short  cells 
which  are  formed  by  one  of  the  ordinary  cells  dividing  into  a  number  of 
disk-shaped  ones  as  shown  in  fig.  147.  The  protoplasm  in  each  antheridium 


150 


MORPHOLOGY. 


forms  two  spermatozoids  (sometimes  only  one)  which  are  of  the  same  form  as 
the  zoogonidia  but  smaller,  and  yellowish  instead  of  green.  In  some  species 

a  motile  body  intermedi- 
ate in  size  and  color  be- 
tween the  spermatozoids 
and  zoogonidia  is  first 
formed,  which  after 
swimming  around  comes 
to  rest  on  the  oogonium, 
or  near  it,  and  develops 
what  is  called  a  "dwarf 
male  pl?nt  "  from  which 
the  reai  spermatozoid  is 
produced. 

318.  Oogonia.  —  The 

gonium  showing  upper  half  oogonia  are   formed   di- 
of  egg  open,  and  a  sperma-  i      r  r     i 

tozoid  ready  to  enter.  (After  rectl7   from    °ne    of   the 
Klebahn).  vegetative  cells.    Inmost 

species  this  cell  first  enlarges  in  diameter,  so  that  it  is  easily  detected.  The 
protoplasm  inside  is  the  egg  cell.  The  oogonium  wall  opens,  a  bit  of  the 
protoplasm  is  emitted,  and  the  spermatozoid  then  enters  and  fertilizes  it 
(fig.  148).  Now  a  hard  brown  wall  is  formed  around  it,  and,  just  as  in  spirogyra 


Fig.  147. 
Portion  ot  thread 
o  f     cedogonium 
showing  antheridia 


Fig.  140- 


150 


Fig.  151. 

Male  nucleus  just  entering  Male  nucleus  fusing  with  The  two  nuclei  fused,  and 
egg  at  left  side.  female  nucleus.  fertilization  complete. 

Figs.  149-151. —  Fertilization  in  cedogonium.     (After  Klebahn). 

a.nd  vaucheria,  it  passes  through  a  resting  period.  At  the  time  of  germinatior 
it  does  not  produce  the  thread-like  plant  again  directly,  but  first  forms  four 
zoospores  exactly  like  the  zoogonidia  (fig.  152).  These  zoospores  ther 
germinate  and  form  the  plant. 

319.  (Edogonium  compared  with  spirogyra. — Now  if  we  compare  cedo- 
gonium with  spirogyra,  as  we  did  in  the  case  of  vaucheria,  we  find  here  also 
that  there  is  an  advance  upon  the  simple  condition  which  exists  in  spiro- 
gyra. Growth  and  division  of  the  thread  is  limited  to  certain  portions.  The 
sexual  organs  are  differentiated.  They  usually  differ  in  form  and  size  from 
the  vegetative  cells,  though  the  oogonium  is  simply  a  changed  vegetative 


CEDOGONIUM.  1 5 1 

cell.  The  sexual  organs  are  differentiated  among  themselves,  the  antheridium 
is  small,  and  the  oogonium  large.  The  gametes  are  also  differentiated  in 
size,  and  the  male  gamete  is  motile,  and  carries  in  its  body  the  nucleus 
which  fuses  with  the  nucleus  of  the  egg  cell. 

But  a  more  striking  advance  is  the  fact  that  the  fertilized  egg  does  not 


Fig*  152. 


Fertilized  egg  of  cedogonium  after  a  period  of  rest  escaping  from  the  wall  of  the  oogonium, 
id  dividing  into  the  four  zoospores.     (After  Juranyi.) 


produce  the  vegetative  thread  of  cedogonium  directly,  but  first  forms  four 

zoospores,  each  of  which  is  then  capable  of  developing  into  the  thread.     On 

the  other  hand  we  found 

that  in  spirogyra  the  zygo- 

spore     develops     directly 

into  the  thread  form  of  the 

plant. 

320.  Position    of    cedo- 
gonium. — GEdogonium    is 
one  of  the  true  thread-like 
algae,  green  in  color,  and 

the    threads    are    divided        pig.  153. 

into    distinct    cells.        It,    Tuft  of  chaeto- 
.  .  ,     .  phora,    natural 

along  with  many  relatives,    size. 

was  once  placed  in  the  old 

genus  conferva.     These  are  all  now  placed  in  the  group 

Confervoidea,  that  is,  the  conferva-like  alga.  Pig  I54 

321.  Relatives  of  cedogonium. — Many  other   genera  Portion  of  chzto phora 
are    related    to   cedogonium.     Some    consist   of  simple     showi"8  branchins- 
threads,   and  others  of  branched  threads.     An    example  of  the    branched 
forms  is  found  in  chsetophora,  represented  in  figures  153,  154.       This  plant 
grows  in  quiet  pools  or  in  slow-running  water.     It  is  attached  to  sticks,  rocks, 
or  to  larger  aquatic  plants.     Many  threads  spring  from  the  same  point  oi 
attachment  and  radiate  in  all  directions.     This,  together  with  the  branching 
of  the  threads,  makes  a  small,  compact,  greenish,  rounded  mass,   which  is 


1 5  2  MORPHOL  OGY. 

held  firmly  together  by  a  gelatinous  substance.  The  masses  in  this  species 
are  about  the  size  of  a  small  pea,  or  smaller.  Growth  takes  place  in  chae- 
tophora  at  the  ends  of  the  threads  and  branches.  That  is,  growth  is  api- 
cal. This,  together  with  the  branched  threads  and  the  tendency  to  form 
cell  masses,  is  a  great  advance  of  the  vegetative  condition  of  the  plant  upon 
that  which  we  find  in  the  simple  threads  of  cedogonium. 


CHAPTER   XVII. 

COLEOCH^TE. 

322.  Among  the  green  algae  coleochaete  is  one  of  the  most 
interesting.      Several  species  are  known  in  this  country.      One 
of  these  at  least  should  be  examined  if  it  is  possible  to  obtain  it. 
It  occurs  in  the  water  of  fresh  lakes  and  ponds,  attached  to 
aquatic  plants. 

323.  The  shield-shaped  coleochsete. — This  plant  (C.  scutata) 


/s 


Fig.  155. 

Stem  o  f 
aquatic  plant 
showing  co- 
leo  c  hae  t  e, 
natural  size. 


Fig.  156. 
Thallus  of  Coleochaete  scutata. 


is  in  the  form  of  a  flattened,  circular,  green  plate,  as  shown  in 
fig.  156.     It  is  attached  near  the  center  on  one  side  to  rushes 


154 


MORPHOLOGY. 


and  other  plants,  and  has  been  found  quite  abundantly  for  sev- 
eral years  in  the  waters  of  Cayuga  Lake  at  its  southern  extremity. 
As  will  be  seen  it  consists  of  a  single  layer  of  green  cells  which 
radiate  from  the  center  in  branched  rows  to  the  outside,  the  cells 
lying  so  close  together  as  to  form  a  continuous  plate.  The  plant 
started  its  growth  from  a  single  cell  at  the  central  point,  and  grew 
at  the  margin  in  all  directions.  Sometimes  they  are  quite  irregu- 
lar in  outline,  when  they  lie  quite  closely  side  by  side  and  inter- 
fere with  one  another  by  pressure.  If  the  surface  is  examined 
carefully  there  will  be  found  long  hairs,  the  base  of  which  is  en- 
closed in  a  narrow  sheath.  It  is  from  this  character  that  the 
genus  takes  its  name  of  coleochsete  (sheathed  hair). 

324.  Fruiting  stage  of  coleochsete. — It  is  possible  at  some 
seasons  of  the  year  to  find  rounded  masses  of  cells  situated  near 
the  margin  of  this  green  disk.     These  have  developed  from  a 
fertilized  egg  which  remained  attached  to  the  plant,  and  prob- 
ably by  this  time  the  parent  plant  has  lost  its  color. 

325.  Zoospore  stage. — This  mass  of  tissue  does  not  develop 
directly  into  the  circular  green  disk,  but  each  of  the  cells  forms 
a  zoospore.      Here  then,   as 

in  cedogonium,  we  have  an- 
other stage  of  the  plant  in- 
terpolated between  the  fer- 
tilized egg  and  that  stage 
of  the  plant  which  bears  the 
gametes.  But  in  coleochsete 
we  have  a  distinct  advance  in 
this  stage  upon  what  is  pres-  Fig.  IS7. 

ent    in    cedogonium,    for    in  .  Portion  of  thallus  of  Co- 

leochaste  scutata,  showing 

coleochsete      the      fertilized  empty  .£ells.  from  which 

zoogonidia   have    escaped, 

egg    develops    first    into    a  °Pj: from  f^Vl11 ;  Z?,°P~ 

t?<-1  A  nicliti    at    tlic    IGtt.       ^Alter 

several -celled  mass  of  tissue  Pringsheim.) 


Fig  158. 

Portion  01  thallus 
of  Coleochaete 
scutata,  showing 
four  antheridia 
formed  from  one 
thallus  cell ;  a  sin- 
;le  spermatozoidat 

e  light.  (After 
Pringsheim.) 


f,! 


before  the  zoospores  are  formed,  while  in  cedogonium  only  four 
zoospores  are  formed  directly  from  the  egg. 

326.   Asexual   reproduction. — In   asexual  reproduction  any  of  the  green 
cells  on  the  plant  may  form  zoogonida.     The  contents  of  a  cell  round  off  and 


COLEOCH&TE. 


'55 


form  a  single  zoogonidium  which  has  two  cilia  at  the  smaller  end  of  the  oval 
body,  fig.  157.  After  swimming  around  for  a  time  they  come  to  rest,  ger- 
minate, and  produce  another  plant. 

327.  Sexual  reproduction. — Oogonium. — The  oogonium  is  formed  by  the 
enlargement  of  a  cell  at  the  end  of  one  of  the  threads,  and  then  the  end  of  the 


Oag— '. 


Fig.  159. 

Coleochaete  soluta ;  at  left  branch  bearing  oogonium  (oog) ;  antheridia  (tint);  egg  in 
oogonium  and  surrounded  by  enveloping  threads  ;  at  center  three  antheridia  open,  and  one 
spermatozoid  ;  at  right  sporocarp,  mature  egg  inside  sporocarp  wall. 

cell  elongates  into  a  slender  tube  which  opens  at  the  end  to  form  a  channel 
through  which  the  spermatozoid  may  pass  down  to  the  egg.  The  egg  is 
formed  of  the  contents  of  the  cell  (fig.  159).  Several  oogonia  are  formed  on 

one  plant,  and  in  such  a 
plant  as  C.  scuta ta  they  are 
formed  in  a  ring  near  the 
margin  of  the  disk. 

328.  Antheridia.— In  C. 
scutata  certain  of  the  cells 
of  the  plant  divide  into  four 
smaller  cells,  and  each  one 
of  these  becomes  an  antheri- 
dium.  In  C.  soluta  the  an- 
theridia grow  out  from  the 


Fig.  160. 


Two    sporocarps     still 


Fig.  161. 

Sporocarp      ruptured      b  i 

surrounde'd     by  "thallus.     growth   of   egg   to    form   cef 

Thallus  finally  decays  and    mass.     Cells    of    this    sporo-  '     .  . 

sets  sporocarp  free.  phyte  forming  zoospores.          end  ot  terminal  cells  in  the 

Figs.i6o,  161.  C.  scutata.  form  of  short  flasks,  some- 

times four  in  number  «-or  less  (fig.  159).      A  single  spermatozoid  is  formed 
from  the  contents.     It  is  oval  and  possesses  two  long  cilia.     After  swim- 


1 56  MORPHOLOG  Y. 

ming   around  it  passes  down  the  tube  of  the  oogonium  and  fertilizes   the 

egg- 

329.  Sporocarp. — After  the  egg  is  fertilized  the  cells  of  the  threads  near 
the  egg  grow  up  around  it  and  form  a  firm  covering  one  cell  in  thickness. 
This  envelope  becomes  brown  and  hard,  and  serves  to  protect  the  egg.  This 
is  the  "fruit"  of  the  coleochsete,  and  is  sometimes  called  a  sporocarp 
(spore  fruit).  The  development  of  the  cell  mass  and  the  zoospores  from  the 
egg  has  been  described  above. 

Some  of  the  species  of  coleochsete  consist  of  branched  threads,  while  others 
form  circular  cushions  several  layers  in  thickness.  These  forms  together 
with  the  form  of  our  plant  C.  scutata  make  an  interesting  series  of  transi- 
tional forms  from  filamentous  structures  to  an  expanded  plant  body  formed 
of  a  mass  of  cells. 


COMPARISON   OF  ALGJZ. 


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CHAPTER  XVIII. 

CLASSIFICATION    AND    ADDITIONAL   STUDIES   OF 
THE   ALG^E. 

In  order  to  show  the  general  relationship  of  the  algae  studied,  the  princi- 
pal classes  are  here  enumerated  as  well  as  some  of  the  families.  In  some 
of  the  groups  not  represented  by  the  examples  studied  above,  a  few  species 
are  described  which  may  serve  as  the  basis  of  additional  studies  if  desired. 
The  principal  classes  *  of  algae  are  as  follows: 

Class  Chlorophyceae. 

331.  These  are  the  green  algae,  so  called  because  the  chlorophyll  green 
is  usually  not  masked  by  other  pigments,  though  in  some  forms  it  is.     There 
are  three  subclasses. 

332.  Subclass  PKOTOCOCCOIDE.^. — In  the  Protococcoideae  are  found  the 
simplest  green  plants.     Many  of  them  consist  of  single  cells  which  live  an 
independent  life.     Others  form  "colonies,"  loose  aggregations  of  individ- 
uals not  yet  having  attained  the  permanency  of  even  a  simple  plant  body, 
for  the  ce\ls  often  separate  readily  and  are  able  to  form  new  colonies.     The 
colonies  are  often  held  together  by  a  gelatinous  membrane,   or  matrix. 
Some  are  motile,  while  others  are  non-motile.     A  few  of  the  families  are 
here  enumerated. 

333.  Family  Volvocaceae. — These  are  all  motile,  during  the  vegetative 
stage.     The  individuals  are  single  or  form  more  or  less  globose  colonies. 

334.  The  "red  snow"  plant  (Sphaerella  nivalis).— This  is  often  found  in 
arctic   and  alpine  regions  forming  a  red  covering  over  more  or  less  large 
areas  of  snow  or  ice.     For  this  reason  it  is  called  the  "red  snow  plant." 

335.  Sphaere'.la  lacustris,  a   closely  related   species,  is  very  widely  dis- 
tributed in  temperate  regions  along  streams  or  on  the  borders  of  lakes  and 


*  In  Engler  &  Prantl's  Pflanzenfamilien,  Wille  uses  the  term  class  for 
these  principal  subdivisions  of  the  algae.  Syshmatists  are  not  yet  agreed 
upon  a  uniform  use  of  the  term?. 

158 


ALG&   CONTINUED:    CLASSIFICATION. 


159 


ponds.  Here  in  dry  weather  it  is  often  found  closely  adhering  to  the  dry 
rock  surface,  and  giving  it  a  reddish  color  as  if  the  rock  were  painted.  This 
is  especially  the  case  in  the  shallow  basins  formed  over  the  uneven  surface 
of  the  rock  near  the  water's  edge.  These  places  during  heavy  rains  or  in 
high  water  are  provided  with  sufficient  water  to  fill  the  basins.  During 
such  times  the  red  snow  plant  grows  and  multiplies,  loses  its  red  color  and 


Sphaerella  lacustris  (^irod.)  Wittrock.  A,  mature  free-swimming  individual 
with  central  red  spot.  B,  division  of  mother  individual  to  form  two.  C,  divi- 
sion of  a  red  one  to  form  four.  D,  division  into  eight.  E,  a  typical  resting  cell, 
red.  F,  same  beginning  to  divide.  G,  one  of  four  daughter  zoospores  after 
swimming  around  for  a  time  losing  its  red  color  and  becoming  green.  (After 
Hazen.) 

becomes  green,  and,  being  motile,  is  free  swimming.  It  is  a  single-celled 
plant,  oval  in  form,  surrounded  by  a  gelatinous  sheath  and  with  two  cilia 
or  flagella  at  the  smaller  end,  by  the  vibration  of  which  it  moves  (fig.  162). 
The  single  cell  multiplies  by  dividing  into  two  cells.  When  the  water  dries 
out  of  the  basin,  the  motile  plant  comes  to  rest,  and  many  of  the  cells  assume 
the  red  color.  To  obtain  the  plant  for  study,  scrape  some  of  the  red  cov- 
ering from  these  rock  basins  and  place  it  in  fresh  spring  water,  and  in  a  da] 
or  so  the  swarmers  are  likely  to  be  found.  Under  certain  conditions  small 
microzoids  are  formed. 

336.  Chlamydomonas  is  a  very  interesting  genus  of  motile  one-celled 
green  algae,  because  the  species  are  closely  related  to  the  Flagellates  among 
the  lower  animals.  The  plant  is  oval,  with  a  single  chloroplast  and  sur- 
rounded by  a  gelatinous  envelope  through  which  the  two  cilia  or  flagella 
extend.  One-celled  organisms  of  this  kind  are  sometimes  called  monads, 
i.e.,  a  one-celled  being.  This  one  has  a  gelatinous  cloak  and  is,  therefore, 
a  cloaked  monad  (Chlamydomonas).  The  species  often  are  found  as  a  very 
thin  green  film  on  fresh  water.  C.  pulvisculus  is  shown  in  fig.  163.  When 
it  multiplies  the  single  cell  divides  into  two,  as  shown  in  B.  Sometimes  a 
non-motile  palmella  stage  is  formed,  as  shown  in  C  and  D.  Reproduction 


i6o 


MORPHOLOGY. 


takes  place  by  gametes  which  are  of  unequal  size,  the  smaller  one  repre- 
senting the  sperm  and  the  larger  one  the  egg   as  in  E  and  F.     These  con- 


Fig.  163. 

Chlamydomonas  pulvisculus  (Mull.)  Ehrb.  A,  an  old  motile  individual;  n, 
nucleus;  p,  pyrenoid;  s,  red  eye  spot;  v,  contractile  vacuole;  B,  motile  indi- 
vidual has  drawn  in  its  cilia  and  divided  into  two;  C,  mother  plant  has  drawn 
in  its  cilia  and  divided  into  four  non-motile  cells;  D,  pamella  stage;  E,  female 
gamete  — egg;  F,  male  gamete  —  sperm ;  G,  early  stage  of  conjugation;  H,  zygo- 
spore  with  conjugating  tube  and  empty  male  cell  attached.  (After  Wille.) 

jugate  as  in  G  and  H,  the  protoplasm  of  the  smaller  one  passing  over  into 
the  larger  one,  and  a  zygospore  is  thus  formed. 

337.  Of  those  which  form  colonies,  Pandorina  morum  is  widely  dis- 
tributed and  not  rare.  It  consists  of  a  sphere  formed  of  sixteen  individuals 

enclosed  in  a  thin  gelatinous  mem- 
brane. Each  cell  possesses  two  cilia 
(or  flagella),  which  extend  from  the 
broader  end  out  through  the  envelop- 
ing membrane.  By  the  movement 
of  these  flagella  the  colony  goes  roll- 
ing around  in  the  water.  When  the 
plant  multiplies  each  individual  cell 
divides  into  sixteen  small  cells,  whkh 
then  grow  and  form  new  colonies. 
Reproduction  takes  place  when  the 
individual  cells  of  the  young  colonies 
separate,  and  usually  a  small  indi- 
vidual unites  with  a  larger  one  and 
a  zygospore  is  formed  (see  fig.  164). 
Eudorina  elegans  is  somewhat  similar, 
but  when  the  gametes  are  formed  cer- 
tain mother  cells  divide  into  sixteen 
small  motile  males  or  sperms,  and 
certain  other  mother  cells  divide  into 
sixteen  large  motile  females  or  eggs. 
These  separate  from  the  colonies,  and 
the  sperms  pair  with  the  eggs  and  fuse  to  form  zygospores.  This  plant  as 
well  as  Chlamydomonas  pulvisculus  foreshadows  the  early  differentiation  of 
sex  in  plants. 


Fig.  164. 

Pandorina  morum  (Mull.)  Bory.  I, 
motile  colony;  II,  colony  divided  into 
16  daughter  colonies;  III,  sexual  colony, 
gametes  escaping;  IV,  V,  conjugating 
gametes;  VI,  VII,  young  and  old  zygo- 
spore; VIII.  zygospore  forming  a  large 
swarm  spore,  which  is  free  in  IX;  X, 
same  large  swarm  spore  divided  to  form 
young  colony.  (After  Pringsheim.) 


ALG^E    CONTINUED:    CLASSIFICATION. 


161 


338.  Family  Tetrasporaceae. — This  family  is  well  represented  by  Tetra- 
spora  lubrica  forming  slimy  green  net-like  sheets  attached  to  objects  in 
slow-running  water.     It  is  really  a  single-celled  plant.     The  rounded  cells 
divide  by  cross  walls  into  four  cells,  and  these  again,  and  so  on,  large  num- 
bers being  held  in  loose  sheets  by  the  slime  in  which  they  are  imbedded. 

339.  Family  Pleurococcaceae. — The  members  of  this  family  are  all  non- 
motile  in  the  vegetative  stage.     They  consist  of  single  individuals,  or  of 
colonies.      Pleurococcus    vulgaris    (Protococcus    vulgaris) 

is  a  single-celled  alga,  usually  obtained  with  little  difficulty. 
It  is  often  found  on  the  shaded,  and  cool,  or  moist  side  of 
trees,  rocks,  walls,  etc.,  in  damp  places.  This  plant  is 
not  motile.  It  multiplies  by  fission  (fig.  165)  into  two, 
then  four,  etc.  These  cells  remain  united  for  a  time,  then 
separate.  Sometimes  the  cells  are  found  growing  out  into 
filaments,  and  it  is  thought  by  some  that  P.  vulgaris  may 
be  only  a  simple  stage  of  a  higher  alga.  Eremosphaera 
viridis  is  another  single-celled  alga  found  in  fresh  water 
among  filamentous  forms.  The  cells  are  large  and  globose. 

340.  Family  Hydrodictyacese. — These    plants    form    colonies    of    cells. 
Hydrodictyon  reticulatum,  the  water  net,  is  made  up  of  large  numbers  of 
cylindrical  cells  so  joined  at  their  ends  as  to  form  a  large  open  mesh  or  net. 
Pediastrum  forms  circular  flat  colonies,  as  shown  in  fig.  1 66.     Both  of  these 


Fig.  165. 
Pleurococcus 
(protococcus) 
vulgaris. 


Fig.  1 66. 

Pediastrum  boryanum.  A,  mature  colony,  most  of  the  young  colonies  have 
escaped  from  their  mother  cells;  at  g,  a  young  colony  is  escaping;  sp,  empDy 
mother  cells;  B,  young  colony;  Ct  same  colony  with  spores  Arranged  in  order. 
(After  Braun.) 

plants  are  rather  common  in  fresh-water  pools,  the  latter  one  intermingled 
with  filamentous  algae,  while  the  former  forms  large  sheets  or  nets.  Mul- 
tiplication in  Hydrodictyon  takes  place  by  the  protoplasm  in  one  of  the  cells 


1 62 


MORPHOLOG  Y. 


dividing  into  thousands  of  minute  cells,  which  gradually  arrange  themselves 
in  the  form  of  a  net,  escape  together  from  the  mother  cell,  and  grow  into  a 
large  net.  In  Pediastrum  multiplication  takes  place  in  a  similar  way,  but 
the  protoplasm  in  each  cell  usually  divides  into  sixteen  small  cells,  and 
escaping  together  from  the  mother  cell  arrange  themselves  and  grow  to  full 
size  (fig.  1 66). 

341.  The  Conjugatese  include  several  families  of  green  algae,  which  prob- 
ably should  be  included  among  the  Chlorophyceae.     They  have  probably 
had  their  origin  from  some  of  the  more  simple  members  of  the  Protococ- 
coideae.     They  are  represented  by  Spirogyra,  Zygnema,  and  the  desmids, 
studied  in  Chapter  14. 

342.  Subclass  CONFERVOIDEJE. — These  are  mostly  filamentous  algae,  the 
filaments  being  composed  of  cells  firmly  united,  and,  with  the  exception  of 
the  simplest  forms,  there  is  a  definite  growing  point.     A  few  of  the  families 
are  as  follows: 

343.  Family  Ulvaceae. — These  contain  the  sea  wracks,  or  sea  lettuce, 

like  Ulva,  forming  expanded 
green,  ribbon-like  growths  in  the 
sea. 

344.  Family  Ulotrichacese, 
represented  by  Ulothrix  sonata, 
not  uncommon  in  slow-running 
water  or  in  ponds  of  fresh  water 
attached  to  rocks  or  wood.  It 
consists  of  simple  threads  of 
short  cells.  Multiplication  takes 
place  by  zoospores.  Repro- 
duction takes  place  by  motile 
-  «  sexual  cells  (gametes)  which 

Fig.  167.  fuse  to  form   a  zygospore  (fig. 

Ulothrix    zonata.     A,   base    of   thread.    B,   j^") 

cells  with  zoospores ,  C ',  one  cell  with  zoospores        ' ' ' 

escaping     another    cell    with     small     biciliate        345.    Family   Cnaetophoraceae. 

gametes    escaping    and    some    fusing    to  form  ,   ,       .^,  ,  ,. 

zygospores,    E.    zoospores    germinating   and  represented  by  Chaetophora   (in 

forming  threads    F,  G,  zygospore  growing  and   Cbxntrr  TC^    and  Dranernanrlin 

forming  zoospores.    (After  Caldwell  and  Dodel-  CnaPte 

Port.)  in  fresh  water. 

346.  Family  (Edogoniacese,  represented  by  (Edogonium  (Chapter  16). 

347.  Family  Coleochaetaceae,  represented  by  Coleochaete  (Chapter  17). 

348.  Subclass  SIPHONE2E. — There  are  several  families. 

349.  Family  Botrydiacese. — This  is  represented  by  Botrydium  granu- 
latum  (Chapter  15,  p.  146). 

•    350.  Family  Vaucheriaceee,  represented  by  Vaucheria  (Chapter  15),  with 
quite  a  large  number  of  species,  is  widely  distributed. 


ALG^E    CONTINUED:    CLASSIFICATION. 


Class  Schizophyceae  (  =  Cyanophyceae). 

351.  The   Blue  Green   Algae,  or  Cyanophyceae  form  slimy  looking  thin 
mats  on  damp  wood  or  the  ground,  or  floating  mats  or  scum  on  the  water. 
The  color  is  usually  bluish  green,  but  in  some  species  it  is  purple,  red  or 
brown.     All  have  chlorophyll,  but  it  is  not  in  distinct  chloroplasts  and  is 
more  or  less  completely  guised  by  the  presence  of  other  pigments.     Two 
orders  and  eight  families  are  recognized.     The  following  include  some  of 
our  common  forms: 

352.  ORDER    COCCOGONALES    (COCCOGONEJE).— Single -celled    plants, 
occurring  singly  or  in  colonies,  in  some  forms 

forming  short  threads.     One  of  the  two  fami- 
lies is  mentioned. 

353.  Family    Chroococcaceae.  —  The    plant? 
multiply  only  through  cell  division.     Chroococ- 
cus,  forms  rounded,  blue-green  cells  enclosed 
in  a  thick  gelatinous  coat,  in  fresh  water  and 
in  damp  places;  certain  species  form  "  lichen  - 
gonidia"  in  some  genera  of  lichens.      Gloeo- 
capsa  is  similar  co  Chroococcus,  but  the  col- 
onies are  surrounded  by  an  additional  common 
gelatinous  envelope  (fig.  168);  on  damp  rocks, 
etc. 

354.  ORDER  HORMOGONALES  (HORMOGONEJE).—  Plants  filamentous, 

simple  celled  or  with  false 
or  true  branching,  usually 
several  celled  (Spirulina  is 
single  celled).  Multiplica- 
tion takes  place  through 
hormogones,  short  sections 
of  the  threads  becoming 
free;  also  through  resting 
cells.  Two  of  the  six  fami- 
lies are  mentioned. 

355.  Family    Oscillatori- 
aceae. — This  family  is  rep- 
resented by  the  genus  Oscil- 
latoria, and  by  several  other 
genera  common  and  widely 
distributed.         Oscillatoria 
many      species, 
are    found    on    the 
damp  ground  or  wood,  or  floating  in  mats  in  the  water.     They  often  form  on 


Fig.  1 68. 
Gloeocapsa. 


Fig.  169. 

A,  Oscillatoria  princeps,    a    terminal  cell;    b,  c. 
portions  from   the   middle  of  a  filament.     In  c,  a 
dead  cell    is  shown    between  the  living  cells;    B, 
Oscillatoria  froelichii,    b,  with  granules  along  the    contains 
partition  walls. 


164 


MORPHOLOGY. 


the  soil  at  the  bottom  of  the  pool,  and  as  gas  becomes  entangled  in  the  mat 
of  threads,  it  is  lifted  from  the  bottom  and  floated  to  the  surface  of  the  water. 
The  plant  is  thread-like,  and  divided  up  into  many  short  cells.  The 
threads  often  show  an  oscillating  movement,  whence  the  name  Oscillator ia. 
356.  Family  Nostocaceae. — This  family  is  represented  by  Nostoc,  which 
forms  rounded,  slimy,  blue-green  masses  on 
wet  rocks.  The  individual  plants  in  the 
slimy  ball  resemble  strings  of  beads,  each 
cell  being  rounded,  and  several  of  these  ar- 
ranged in  chains  as  shown  in  fig.  170.  Here 
and  there  are  often  found  larger  cells  (hetero- 
cysts)  in  the  chain.  Nostoc  punctiforme 
lives  in  the  intercellular  spaces  of  the  roots 
of  cycads  (often  found  in  greenhouses),  and 
in  the  stems  of  Gunnera.  N.  sphaericum 
lives  in  the  spaces  between  the  cells  in  many 
species  of  liverworts  (in  the  genera  Antho- 
ceros,  Blasia,  Pellia,  Aneura,  Riccia,  etc.), 
and  in  the  perforated  cells  of  Sphagnum 
acutifolium.  Anabaena  is  another  common 
and  widely  distributed  genus.  The  species 
occur  in  fresh  or  salt  water,  singly  or  in  slimy 
Anabaena  azollae  lives  endophyti- 
cally  in  the  leaves  of  the  water  fern,  Azolla. 


Nostoc    linckii. 


filament 


with  two  heterocysts  (h),  and  a  masses, 
large  number  of  spores  (sp); 
B,  isolated  spore  beginning  to 
germinate;  C,  young  filament 
developed  from  spore.  (After 
Bornet.) 


Class  Schizomycetes. 


357.  Bacteriales. — The  bacteria  are  sometimes  classified  with  the  Cyano- 
phyceae,  under  the  name  Schizophyta,  and  represent  the  subdivision  Schiz- 
omycetes, or  fission  fungi,  because 
many  of  them  multiply  by  a  divis- 
ion of  the  cells  just  as  the  blue -green 
algae  do.  For  example,  Bacillus 
forms  rods  which  increase  in  length 
and  divide  into  two  rods,  or  it  may 
grow  into  a  long  thread  of  many 

short  rods.     Micrococcus  consists  F*£-  I?1- 

,     .      ,  j   j       11          04-  Bacteria.      A,   Bacillus  subtilis.      Spores 

of  single  rounded  cells.      Strepto-  in  threadSi  unstained  rods,  and  stained  rods 

coccus    forms    chains   of    rounded  showing  cilia;    B .Bacillus  tetani, .the  teta- 
nus or   lockjaw   bacillus,    round   in   garden 

cells,  Sarcina  forms  irregular  cubes  soil  and  on  old  rusty  nails.     Spores  in  club- 
,  j    j       11          u-i       iU        1-1       shaped  ends.     C,  Micrococcus;    D,  Sarcina; 

of  rounded  cells,  while  others  like  £>   streptococcus;     F,   Spirillum.      (After 

Spirillum     are     spiral     in     form.  Migula.) 

Bacillus  subtilis  may  be  obtained  by  making  an  infusion  from  hay  and 


ALG&   CONTINUED:    CLASSIFICATION.  165 

allowing  it  to  stand  for  several  days.  Bacillus  tetani  occurs  in  the  soil,  on 
old  rusty  nails,  etc.  It  is  called  the  tetanus  bacillus  because  it  causes  a 
permanent  spasm  of  certain  muscles,  as  in  "lockjaw."  This  bacillus 
grows  and  produces  this  result  on  the  muscles  when  it  occurs  in  deep  and 
closed  wounds  such  as  are  caused  by  stepping  on  an  old  nail  or  other  object 
which  pierces  the  flesh  deeply.  In  such  a  deep  wound  oxygen  is  deficient, 
and  in  this  condition  the  bacillus  is  virulent.  Opening  the  wounds  to 
admit  oxygen  and  washing  them  out  with  a  solution  of  bichloride  of  mer- 
cury prevents  the  tetanus.  Many  bacteria  are  of  great  importance  in  bring- 
tag  about  the  decay  of  dead  animal  and  plant  matter,  returning  it  to  a  con- 
dition for  plant  food.  (See  also  nitrate  and  nitrite  bacteria,  Chapter  IX.) 
While  rt/ost  bacteria  are  harmless  there  are  many  which  cause  very  serious 
diseases  of  man  and  animals,  as  typhoid  fever,  diphtheria,  tuberculosis,  etc., 
while  some  others  produce  disease  in  plants.  Others  aid  in  certain  fer- 
mentations or  liquids  and  are  employed  for  making  certain  kinds  of  wines 
or  other  beverages.  Some  work  in  symbiosis  with  yeasts,  as  in  the  kephir 
yeast,  used  in  femr«riumg  certain  crude  beverages  by  natives  of  some  coun- 
tries. 

357a.  Myxobacteriales  (Utyxobacteria^ese  Thaxter  *). — These  plants  con- 
sist of  colonies  of  bacteria-tike  organisms,  motile  rods,  which  multiply  by 
cross-division  and  secrete  a  gelatinous  substance  or  matrix  which  surrounds 
the  colonies.  They  form  plasmodium-like  masses  which  superficially 
resemble  the  slime  moulds.  In  the  fruiting  stage  some  species  become 
elevated  from  the  substratum  into  cylindrical,  clavate,  or  branched  forms, 
which  bear  cysts  of  various  shapes  containing  the  rods  in  a  resting  stage, 
or  the  rods  are  converted  into  spore-like  masses.  Ex.,  Chondromyces 
crocatus  on  decaying  plant  parts,  Myxobacter  aureus  on  wet  wood  and 
bark,  Myxococcus  rubescens  on  dung,  decaying  lichens,  paper,  etc. 

Class  Flagellata. 

358.  The  flagellates  are  organisms  of  very  low  organization  resembling 
animals  as  much  as  they  do  plants.  They  are  single  celled  and  possess  two 
cilia  or  flagella,  by  the  vibration  of  which  they  move.  Some  are  without  a 
cell  wall,  while  others  have  a  well-defined  membrane,  but  it  rarely  consists 
of  cellulose.  Some  have  chromatophores  and  are  able  to  manufacture 
carbohydrates  like  ordinary  green  plants.  These  are  green  in  Euglena, 
and  brown  in  Hydrurus.  Some  possess  a  mouth-like  opening  and  are  able 
to  injest  solid  particles  of  food  (more  like  animals),  while  others  have  no 
such  opening  and  absorb  food  substances  dissolved  in  water  (more  like 
plants).  The  Euglena  viridis  is  not  uncommon  in  stagnant  water,  often 
forming  a  greenish  film  on  the  water. 


*  See  Bot.  Gaz.,  17,  389,  1892. 


i66 


MORPHOLOGY. 


Class  Peridineae. 

3580.  These  are  peculiar  one-celled  organisms  provided  with  two  flagella 
and  show  some  relationship  to  the  Flagellates.  They  usually  are  provided 
with  a  cellulose  membrane,  which  in  some  forms  consists  of  curiously 
sculptured  plates.  In  the  higher  forms  this  cellulose  membrane  consists  of 
two  valves  fitting  together  in  such  a  way  as  to  resemble  some  of  the  diatoms. 
Like  the  Flagellates,  some  have  green  chromatophores,  which  in  some  are 
obscured  by  a  yellow  or  brown  pigment  (resembling  the  diatoms),  while 
still  others  have  no  chlorophyll.  The  Peridinese  are  abundant  in  the  sea, 
while  some  are  found  in  fresh  water. 

Class  Diatomaphyceae  (Bacillariales,  Diatomaceae). 

3586.  The  diatoms  are  minute  and  peculiar  organisms  believed  to  be 
algae.  They  live  in  fresh,  brackish,  and  salt  water.  They  are  often  found 
covering  the  surface  of  rocks,  sticks,  or  the  soil  in  thin  sheets.  They  occur 
singly  and  free,  or  several  individuals  may  be  joined  into  long  threads,  or 
other  species  may  be  attached  to  objects  by  slender  gelatinous  stalks.  Each 


Fig.  1710. 

A  group  of  Diatoms:  c  and  d,  top  and  side  views  of  the  same  form;  e,  colony 
of  stalked  forms  attached  to  an  alga;  f  and  g,  top  and  side  views  of  the  form  shown 
at  e\  h,  a  colony;  *',  a  colony,  the  top  and  side  view  shown  at  k  and  «,  forming  auxo- 
spores.  (After  Kerner.) 

protoplast  is  enclosed  in  a  silicified  skeleton  in  the  form  of  a  box  with  two 
halves,  often  shaped  like  an  old-fashioned  pill  box,  one-half  fitting  over  the 
other  like  the  lid  of  a  box.  It  is  evident  that  in  this  condition  the  plant 
cannot  increase  much  in  size. 

They  multiply  by  fission.  This  takes  place  longitudinally,  i.e.,  in  the 
direction  of  the  two  halves  or  valves  of  the  box.  Each  new  plant  then  has  a 
valve  only  on  one  side.  A  new  valve  is  now  formed  over  the  naked  half, 
and  fits  inside  the  old  valve.  At  each  division  the  individuals  thus  become 
smaller  and  smaller  until  they  reach  a  certain  point,  when  the  valves  are 
cast  off  and  the  cell  forms  an  auxospore,  i.e.,  it  grows  alone,  or  after  conju- 
gation with  another,  to  the  full  size  again,  and  eventually  provides  itself 


ALG&   CONTINUED:    CLASSIFICATION. 


i67 


vrith  new  valves.  The  valves  are  often  marked  with  numerous  and  fine 
lines,  often  making  beautiful  figures,  and  some  are  used  for  test  objects  for 
microscopes. 

The  free  forms  are  capable  of  movement.  The  movement  takes  place  in 
the  longitudinal  direction  of  the  valves.  They  glide  for  some  time  in  one 
direction,  and  then  stop  and  move  back  again.  It  is  not  a  difficult  thing  to 
mount  them  in  fresh  water  and  observe  this  movement. 

The  diatoms  have  small  chlorophyll  plates,  but  the  green  color  is  dis- 
guised by  a  brownish  pigment  called  diatomin.  The  relationships  of  the 
diatoms  are  uncertain,  but  some,  because  of  the  color,  think  they  are  re- 
lated to  the  Phaeophyceae. 

Class  Phaeophyceae. 

369.  The  brown  algae.  (Phaeophyceae). — The  members  of  this  class  pos- 
sess chlorophyll,  but  it  is  obscured  by  a  brown  pig- 
ment. The  plants  are  accessible  at  the  seashore, 
and  for  inland  laboratories  may  be  preserved  in 
formalin  (2^  per  cent).  (See  also  Chapter  LVI.) 

360.  Ectocarpus. — The  genus  Ectocarpus  repre- 
sents well  some  of  the  simpler  forms  of  the  brown 
algae  (fig.  172).  They  are  slender,  filamentous 
branched  algae  growing  in  tufts,  either  epiphytic  on 
other  marine  algae  (often  on  Fucaceae),  or  on  stones. 
The  slender  threads  are  only  divided  crosswise, 
and  thus  consist  of  long  series  of  short  cells.  The 
sporangia  are  usually  plurilocular  (sometimes  uni- 


Fig.  172. 

A,  Ectocarpus  siliculosus;  B,  branch  with  a  young  and  a  ripe 
plurilocular  sporangium;  E,  gametes  fusing  to  form  zygospore. 
(B,  after  Thuret;  £,  after  Berthold.) 


i68 


MORPHOLOGY. 


locular),  and  usually  occur  in  the  place  of  lateral  branches.  The  zoospores 
escape  from  the  apex  of  the  sporangium  and  are  biciliate,  and  they  fuse  to 
form  zygospores. 

361.  Sphacelaria. — The  species  of  this  genus  repre- 
sent an  advance  in  the  development  of  the  thallus. 
While  they  are  filamentous  and    branched,  division 
takes  place  longitudinally  as  well  as  crosswise  .(fig. 

173). 

362.  Leathesia  difformis  represents  an    interesting 
type  because  the  plant  body  is  small,  globose,  later 
irregular  and  hollow,  and  consists  of  short  radiately 
arranged  branches,  the   surface  ones  in    the  form  of 
short,  crowded,  but  free,  trichome-like  green  branches. 

This  trichothallic  body  recalls  the  similar    form    of 
Sphacelana,   portion  ,  .  .,         .        ,„,  ,x  , 

of  plant  stowing  longi- Chaetophora    pisiformis     (Chapter    16)     among    the 
tudinal  division  of  cells,  rv^r^Wr-^ 


Fig.  173- 


and  brood  bud  (pluri- 

locular  sporangium).          363.  The  Giant  Kelps. — Among  the   brown    algae 

are    found    the    largest    specimens,    some    of    the    laminarias     or    giant 

kelps,    rivaling  in    size  the    largest    land    plants, 

and  some  of  them  have  highly  developed  tissues. 

Postelsia  palma/ormis  has  a  long,  stout  stem,  from 

the  free  end  of  which  extend  numerous  large  and 

long  blades,  while  the  stem  is  attached  to  the  rocks 

by  numerous  "root"  like  outgrowths,  the  holdfasts. 

It  occurs   along    the    northern  Pacific  coast,  and 

appears  to  flourish  where  it  receives  the  shock  of 

the  surf  beating  on  the  shore.     Several  species  of 

Laminaria  occur  on  our  north  Atlantic  coast.     In 

L.   digitata,  the  stem  expands  at   the  end  into  a 

broad    blade,  which    becomes    split    into    several 

smaller   blades    (fig.    174).      Macrocystis    pyrifera 

inhabits  the  ocean  in  the  southern  hemisphere,  and 

sometimes    is    found    along    the    north    American 

coast.      It  is  said    to  reach   a  length  of    200—300 

meters. 

364.  Fucus,  or  Rockweed.— This  plant  is  a  more  pig 

or  less  branched  and  flattened  thallus  or  "frond."       Laminaria        digitata, 
One   of    them,    illustrated    in    fig.    119,    measures  |°rama  (R^ced*;    N°rth> 


(6-i2  inches)  in  length.  It  Is  attached  to 
rocks  and  stones  which  are  more  or  less  exposed  at  low  tide.  From  the  base 
of  the  plant  are  developed  several  short  and  more  or  less  branched  expansions 
called  "holdfasts,"  which,  as  their  name  implies,  are  organs  of  attachment. 
Some  species  (F.  vesiculosus)  have  vesicular  swellings  in  the  thallus. 


A    G&   CONTINUED:    CLASSIFICATION. 


169 


The  fruiting  portions  are  somewhat  thickened  as  shown  in  the  figure. 
Within  these  portions  are  numerous  oval  cavities  opening  by  a  circular  pore, 
which  gives  a  punctate  appearance  to  these  fruiting  cushions.  Tufts  of  hairs 
frequently  project  through  them. 

365.  Structure  of  the  conceptacles. — On  making  sections  of  the  fruiting 
portions  one  finds  the  walls  of  the  cavities  covered  with  outgrowths.  Some 
of  these  are  short  branches  which  bear  a  large  rounded  terminal  sac,  the 


Fig.  177. 

Oogonium     of     Fucus 
with  ripe  eggs. 


Fig.  I7S- 

Portion  of  plant  of  Fucus  show- 
ing conceptacles  in  enlarged  ends; 
and  below  the  vesicles  (Fucus 
resiculosus). 


Fig.  176. 

Section    of    conceptacle    of  Fucus,    showing 
oogonia,  and  tufts  of  antheridia. 

oogonium,  at  maturity  containing  eight  egg  cells.  More  slender  and  much- 
branched  threads  bear  narrowly  oval  antheridia.  In  these  are  developed 
several  two-ciliated  spermatozoids. 

366.  Fertilization.— At  maturity  the  spermatozoids  and  egg  cells  float  out- 
side of  the  oval  cavities,  where  fertilization  takes  place.     The  spermatozoid 


MORPHOLOGY. 


sinks  into  the  protoplasm  of  the  egg  cell,  makes  its  way  to  the  nucleus  of 
the  egg,  and  fuses  with  it  as  shown  in  fig.  181.  The  fertilized  egg  then 
grows  into  a  new  plant.  Nearly  all  the  brown  algae  are  marine. 


Fig.  178.  Fig.  179.  Fig.  1 80. 

Antheridia  of  Fucus,  on         Antheridia  of  Fucus  with         Eggs  of  Fucus  surround- 
branched  threads.  escaping  spermatozoids.          ed  by  spermatozoids. 


Fig.  181. 

Fertilization  in  Fucus;  fn,  female  nucleus;  win,  male  nucleus;  n,  nucleolus.  In 
the  left  figure  the  male  nucleus  is  shown  moving  down  through  the  cytoplasm  of  the 
egg;  in  the  remaining  figures  the  cytoplasm  of  the  egg  is  omitted.  (After  Stras- 
burger.) 

367.  The   Gulf   weed   (Sargassum   bacciferum)    in  the  warmer  Atlantic 
ocean  unites  in  great  masses  which  float  on  the  water,  whence  comes  the 
name  "Sargassum  Sea."     The  Sargassum  grows  on  the  coast  where  "it  is 
attached  to  the  rocks,  but  the  beating  of  the  waves  breaks  many  specimens 
loose  and  these  float  out  into  the  more  quiet  waters,  where  they  continue 
to  grow  and  multiply  vegetatively. 

368.  Uses. — Laminaria  japonica  and  L.  angustata  are  used  as  food  by 
the  Chinese  and  Japanese.     Some  species  of  the  Laminariaceae  are  used  as 
food  for  cattle  and  are  also  used  for  fertilizers,  while  L.  digitata  is  some- 
times employed  in  surgery. 


ALG&   CONTINUED:    CLASSIFICATION. 


171 


Classification. — Kjellman  divides  the  Phaeophyceae  into  two  orders. 

369.  Order   Phaeosporales    (Phaeosporeae)  including  18  families.     One  of 
the  most  conspicuous  families  is  the  Laminariaceae,  including  among  others 
the  Giant  Kelps  mentioned  above  (Laminaria,  Postelsia,  Macrocystis,  etc.). 

370.  Order   Cyclosporales    (Cyclosporeae). — This  includes  one  family,  the 
FucacecB  with  Ectocarpus,  Sphacelaria,  Laeathesia,  Fucus,  Sargassum,  etc. 


Class  Rhodophyceae. 

371.  The  red  algae  (Rhodophyceae). — The  larger  number  of  the  so-called 
red  algae  occur  in  salt  water,  though  a  few  genera  occur  in  fresh  water. 
The  plants  possess  chlorophyll,  but  it  is  usually  obscured  by  a  reddish  or 
purple  pigment. 

372.  Nemal  on. — This  is  one  of  the  lower  marine  forms,  though  its  thal- 
lus  is   not  one  of  the   simplest   in  struc- 
ture.      The    plant    body    consists    of   a 

slender  cylindrical  branched  shoot,  some- 
times   very   profusely    branched.       The 
central   strand   is  rather  firm,  while  the 
cortex   is   composed  of  rather  loose  fila-   a 
ments. 

373.  Batrachospermum. — This    genus 
occurs   in  fresh  water,    and   the  species 
are    found    in     slow-running    water    of 
shallow  streams  or  ditches.     There  is  a 
central  slender  strand  which  is  more  or 
less    branched,    and    on    these   branches 
are   whorls   of   densely  crowded  slender 
branches   occurring  at  regular   intervals. 
The    plants    are    usually    very    slippery. 
Gonidia  are  formed  on  the  ends  of  some 
of  these  branches  in  globose,  sporangia, 
called  monosporangia,  since  but  a  single 
spore  or  gonidium  is  developed  in  each. 
Other  branches  often  terminate  in  long 

slender  hyaline  setae. 

*tA    r*.~  TM.'  i  a  cystocarp  (o),  the   trichogyne  (t) 

374.  Lemanea.— Tins  genus  also  occurs  still  showing;  C,  an  almost  mature 

in    fresh    water.      The    species    develop 

only  during  the  cold   winter  months  in 

rapids  of  streams  or  where  the  water  from  falls  strikes  the  rocks  and  is 

thoroughly  aerated.      They  form  tufts  of  greenish  threads,  cylindrical  or 

whiplike,  which  in    the  summer  are  usually  much  broken  down.       The 

threads  are  hollow  and  have  a  firm  cortex.     These  are  the  sexual  shoots, 


two  spermatia  (s);  B,  beginning  of 


MORPHOLOG  Y. 


and  they  arise  as  branches  from  a  sterile  filamentous -branched,  Chantransia- 
like  form. 

375.  Fertilization  in  the  lower  red  algse. — The  sexual  organs  in  the  red 
algae  consist  of  antheridia  and  carpogonia.  The  antheridia  are  usually 
borne  in  crowded  clusters,  or  surfaces,  and  bear  terminally  the  small  non- 
motile  sperm  cells.  The  carpogonium  is  a  branch  of  one  or  several  cells, 
the  terminal  cell  (procarp)  extending  into  a  long  slender  process,  the  tri_ 
chogyne.  The  sperm  cell  comes  in  contact  with  the  trichogyne,  and  in  the 
case  of  Nemalion  and  some  others  the  nucleus  has  been  found  to  pass  down 
the  inside  and  fuse  with  the  nucleus  of  the  procarp. 

From  this  point  in  the  lower  red  algae  like  Nemalion,  Batrachospermum 


Fig.  183. 

A,  part  of  a  shoot  showing  whorls  of  branches  with  clusters  of  carpospores. 
B.  carpogonic  branch  or  procarp:  c,  procarp  cell;  tr,  trichogyne.  C,  same  with 
sperm  (sp)  uniting  with  trichogyne.  D,  same  with  carpospores  developing  from 
procarp  cell.  E,  male  branch  with  one-celled  antheridia.  F,  same  with  some  of 
antheridia  empty.  (After  Schmit'z. ) 

and  Lemanea  the  formation  of  the  spores  is  very  simple.  The  procarp  is 
Stimulated  to  growth,  and  buds  in  different  directions,  producing  branched 
chains  of  spores  (carpospores).  The  carpospores  form  a  rather  compact 


CONTINUED:    CLASSIFICATION. 


'73 


cluster  called  the  sporocarp,  which  means  spore-fruit  or  spore-fruit  body. 
In  Batrachospermum  it  is  seen  as  a  compact  tuft  in  the  loose  branching,  in 
Nemalion  it  lies  in  the  surface  of  the  cortex,  while  in  Lemanea  the  sporo- 
carps  lie  at  different  positions  in  the  hollow  tube  of  the  sexual  shoot. 

376.  Gonidia  in  the  red  algae. — The  common  type  of  gonidium  in  the  red 
alg:e  is  found  in  the  tetraspores.  A  single  mother  cell  divides  into  four  cells 
arranged  usually  in  the  form  of  tetrads  within  the  tctrasporangium.  In 
Callithamnion  the  tetrasporangium  is  exposed.  In  Polysiphonia,  Rhab- 


A 


Fig.  184. 

A  red  alga  (Callithamnion),  showing  spor- 
angium A,  and  the  tetraspores  discharged 
B.  (After  Thuret.) 


Fig.  185. 

Gracilaria,  portion  of  frond, 
showing  position  of  cystocarps. 


Fig.  1 86. 

Gracilaria,  section  of  cysto- 
carp  showing  spores. 


donia,  Gracilaria,  etc.,  it  is  imbedded  in  the  cortex.  In  Batrachospermum 
there  are  monosporangia,  each  monosporangium  containing  a  single  goni* 
diu»i,  while  in  Lemanea,  and  according  to  some  also  in  Nemalion,  gonidia 
are  wanting. 


174 


MORPHOLOG  Y. 


377.  Gracilaria. — Gracilaria  is  one  of  the  marine  forms,  and  one  species 
is  illustrated  in  fig.  185.     It  measures  i$-2ocm  or  more  long,  and  is  pro- 
fusely branched  in  a  palmate  manner.     The  parts  of  the  thallus  are  more 
or  less  flattened.     The  fruit  is  a  cystocarp,  which  is  characteristic  of  the 
Rhodophyceae  (Florideae).     In   Gracilaria    these  fruit  bodies  occur  scat- 
tered over  the  thallus.     They  are  somewhat  flask -shaped,  are  partly  sunk 
in  the  thallus,  and  the  Conical  end  projects  strongly  above  the  surface.     The 
carpospores  are  grouped  in  radiating  threads  within  the  oval  cavity  of  the 
cystocarp.     These  cystocarps  are  developed  as  a  result  of  fertilization. 
Other  plants  bear  gonidia  in  groups  of  four,  the  so-called  tetraspores. 

378.  Rhabdonia. — This  plant  is  about  the  same  size   as  the  gracilaria, 
though  it  possesses  more  filiform  branches.     The  cystocarps  form  prom- 
inent elevations,  while  the  carpospores  lie  in  separated  groups  around  the 


Fig.  187. 

Rhabdonia,  branched 
portion  of  frond  show- 
ing cystocarps. 


Fig.  1 88. 

Section  of  cystocarp  of  rhabdonia,  showing 
spores. 


periphery  of  a  sterile  tissue  within  the  cavity.     (See  figs.  187,  188.)     Goni- 
dia in  the  form  of  tetraspores  are  also  developed  in  Rhabdonia. 

379.  Fertilization  of  the  higher  red  algse. — The  process  of  fertilization  in 
most  of  the  red  algae  is  very  complicated,  chiefly  because  the  fertilized  egg 
cell  (procarp)  does  not  develop  the  spores  directly,  as  in  Nemalion,  Le- 


ALG&   CONTINUED:    CLASSIFICATION. 


175 


manea,  etc.,  but  fuses  directly,  or  by  a  short  cell  or  long  filament  with  one 
or  more  auxiliary  cells  before  the  sporocarp  is  finally  formed.  Examples 
are  Rhabdonia,  Polysiphonia, 
Callithamnion,  Dudresnaya, 
etc.  (fig.  189).  The  auxiliary 
cell  then  develops  the  sporo- 
carp. See  fig.  189  for  conju- 
gation of  a  filament  from  the 
fertilized  procarp  with  an  aux- 
iliary cell. 

380.  Uses  of  the  red  algae. — 
Many  species  produce  a  great 
amount    of    gelatinous     sub- 
stance  in    their   tissues,    and 
several  of  these  are  used  for 
food,   for  the  manufacture  of. 
gelatines  and  agar-agar.    Some* 
of  these  are   Gracilaria   lich- 
enoides  and  wrightii,  the  for- 
mer   species    occurring   along 
the  coast  of  India  and  China. 
The  plant  is  easily  converted 
into       gelatinous       substance 

(agar-agar).       Chondrus    cris-    which   grows  out  from  below  the1  base  of  the 

..  ,      ..      .,          .   .       .        trichogyne,  and  comes  iajcontact  with  the  fertile 

pus,  widely  distnbuted  in  the    branches/,  f:  c*', young%nnecting-tube.    (After 

northern  Atlantic  is  known  as    Thuret  and  Bornet-> 

"Irish"  moss  and  is  used  for  food  and  for  certain  medicinal  purposes. 
Gigartina  mamillosa  in  the  Atlantic  and  Arctic  oceans  is  similarly  em- 
ployed. The  following  orders  are  recognized  in  the  red  algae: 

381.  Order    Bangiales. — Example,    Bangia  atropurpurea   (=  Conferva 
atropurpurea)  in  springs  and  brooks  in  North  America  and  Europe.      Por- 
phyra  contains  a  number  of  species  forming  broad,  thin,  leaf-like  purple 
sheets  in  the  sea. 

382.  Order    Nemalionales.  —  Including     Lemanea,     Batrachospermum, 
Nemalion,  described  above,  and  many  others. 

383.  Order   Gigartinales. — In    this    order  occurs    the  common    Iceland 
moss  (Chondrus  crispus)  in  the  sea,  and   Rhabdonia  and   GigartiTia  men- 
tioned above. 

384.  Order   Bhodomeniales. — In  this  order  occurs    Gracilaria  and  Poly- 
siphonia mentioned  above,  also  the  beautiful  marine  forms  like  Ceramium. 

385.  Order  Cryptonemiales.  —  Examples    are    Dudresnaya,    Melobesia, 
Corallina,  etc.,  the  last  two  genera  include  many  species  with  a  wide  dis- 
tribution. 


Fig.  189. 

Dudresnaya  purpurifera.    tr,  trichogyne,  with 
sperm      cells      attached;     ct,    connecting-tube 


MORPHOLOG  Y. 


Class  Charophyceae,  Order  Charales. 

386.  The  Charales  are  by  some  thought  to  represent  a  distinct  class  of 
algae  standing  near  the  mosses,  perhaps,  because  of  the  biciliate  character  of 
the  spermatozoids.  There  is  one  family,  the  Characeae.  The  plants  occur 
in  fresh  and  brackish  water.  Aside  from  the  peculiarity  of  the  reproductive 
organs  they  are  remarkable  for  the  large  size  of  the  cells  of  the  internodes 
and  of  the  "leaves,"  and  the  protoplasm  exhibits  to  a  remarkable  degree 

the  phenomenon  of  "cyclosis" 
(see  paragraphs  17-20).  Three 
of  the  genera  are  found  in  North 
America  (Chara,  Nitella  (Fig.  8) 
and  Tolypella). 

386a.  The  complicated  struc- 
ture of  the  sexual  organs  shows  a 
higher  state  of  organization  than 
any  of  the  other  living  algae 
known.  While  the  internodes  in 
Nitella  are  composed  of  a  single, 
stout  cell,  some  times  a  foot  or 
more  in  length,  the  nodes  in  all  are 
composed  of  a  group  of  smaller 
cells.  From  the  lateral  cells  of 
this  group  lateral  axes  (sometimes 

Fis-  ^2a-  called  leaves)  arise  in  whorls. 
Reproductive  organs  of  Chara  fragilis.    A,        T      -,.     „        ,       . 
a  central  portion  of  a  leaf,  b,  with  an  anther-       In   Nitella   the  internodes  are 

idium,  a,  and  a  carpogonium,  s,  surrounded  nf,T,PH      K,,t    in    rnn«t    cnpnVc    rA 

by  the  spirally  twisted  enveloping  cells;  c,  nakecl>     c  most    species    Of 

crown  of  five  cells  at  apex;   /?,  sterile  lateral  Chara  they  are  corticated,  i.e.,  they 
leaflets;  0'  large  lateral  leaflet  near  the  fruit;  ,. 

/?'/,  bracteoles  springing  from  the  basal  node  are  covered  by  a  layer  of  numer- 

cells  which 


sk;  w,  nodal  cell  of  leaf;  u,  intermediate  downward  from  the  nodes  at  the 
cell  between  w  and  the  basal -node  cell  of  ,  ...  ,  ,  . . 

the  antheridium;  /,  cavity  of  the  internode    base  of  the  whorl  of  lateral  shoots, 
of  the   leaf;     br,  cortical   cells   of  the  leaf.         QQRV.     TV.O    c^-vnol    r 
AX  about  33;   5X24o.     (After  Sachs.)  6l)-   The    sexual    organs   are 

situated    at    the    nodes    of    the 

whorled  lateral  shoots,  and  consist  of  antheridia  and  carpogonia.  Most  of 
the  plants  are  monoscious,  and  both  antheridia  and  carpogonia  are  ofteir 
attached  to  the  same  node,  the  antheridium  projecting  downward  while  the 
carpogonium  is  more  or  less  ascending.  The  sexual  organs  are  visible 
to  the  unaided  eye.  The  antheridium  is  a  globose  red  body  of  an  exceed- 
ingly complicated  structure.  The  sperms  are  borne  in  several  very  long 
coiled  slender  threads  which  are  divided  transversely  into  numerous  cells. 
The  carpogonium  is  oval  or  elliptical  in  outline,  the  wall  of  which  is  com- 
posed of  several  closely  coiled  spiral  threads  enclosing  the  large  egg. 


CHAPTER  XIX. 

FUNGI :  MUCOR  AND  SAPROLEGNIA. 

Mucor. 

387.  In  the  chapter  on  growth,  and  in   our  study   of  proto- 
plasm, we  have  become  familiar  with  the  vegetative  condition  of 
mucor.     We  now  wish  to  learn  how  the  plant  multiplies  and  re- 
produces itself.     For  this  study  we  may  take  one  of  the  mucors. 
Any  one  of  several  species  will  answer.     This  plant  may  be  grown 
by  placing  partially  decayed  fruits,  lemons,  or  oranges,  from  which 
the  greater  part  of  the  juice  has  been  removed,  in  a  moist  cham- 
ber ;  or  often  it  occurs  on  animal  excrement  when  placed  under 
similar  conditions.      In  growing  the  mucor  in  this  way  we  are 
likely  to  obtain  Mucor   mucedo,    or   another    plant  sometimes 
known  as  Mucor  stolonifer,  or  Rhizopus  nigricans,  which  is  illus- 
trated in  fig.  191.     This  latter  one  is  sometimes  very  injurious  to 
stored  fruits  or  vegetables,  especially  sweet  potatoes  or  rutaba- 
gas.    Fig.  190  is  from  a  photograph  of  this  fungus  on  a  banana. 

388.  Asexual  reproduction. — On  the  decaying  surface  of  the 
vegetable  matter  where  the  mucor  is  growing  there  will  be  seen 
numerous  small  rounded  bodies  borne   on  very  slender  stalks. 
These  heads  contain  the  gonidia,  and  if  we  sow  some  of  them  in 
nutrient  gelatine  or  agar  in  a  Petrie   dish  the  material  can  be 
taken  out  very  readily  for  examination   under  the  microscope. 
Or  we  may  place  glass  slips  close  to  the  growing  fungus  in  the 
moist  chamber,  so  that  the  fungus  will  develop  on  them,  though 
cultures  in  a  nutrient  medium  are  much  better.    Or  we  may  take 
rV"*  material  directly  from  the  substance  on  which  it  is  growing. 

177 


178  MORPHOLOGY. 

After  mounting  a  small  quantity  of  the  mycelium  bearing  these 
heads,  if  we  have  been  careful  to  take  it  where  the  heads  appear 
quite  young,  it  may  be  possible  to  study  the  early  stages  of  their 


Fig.  190. 
Portion  of  banana  with  a  mould  (Rhizopus  nigricans)  growing  on  one  end. 

development.  We  shall  probably  note  at  once  that  the  stalks  or 
upright  threads  which  support  the  heads  are  stouter  than  the 
threads  of  the  mycelium. 

These  upright  threads  soon  have  formed  near  the  end  a  cross 
wall  which  separates  the  protoplasm  in  the  end  from  the  remain- 
der. This  end  cell  now  enlarges  into  a  vesicle  of  considerable 
size,  the  head  as  it  appears,  but  to  which  is  applied  the  name  of 
sporangium  (sometimes  called  gonidangium),  because  it  encloses 
the  gonidia. 

At  the  same  time  that  this  end  cell  is  enlarging  the  cross  wall 
is  arching  up  into  the  interior.  This  forms  the  columella.  All 
the .  protoplasm  in  the  sporangium  now  divides  into  gonidia. 
These  are  small  rounded  or  oval  bodies.  The  wall  of  the  spo- 


FUNGI:    MUCOK.  1 79 

rangium  becomes  dissolved,    except   a  small  collar  around  the 
stalk  which   remains  attached  below  the  columella  (fig.  192). 


Fig.  191. 

Group  of  sporangia  of  a  mucor  (Rhizopus  nigricans)  showing  rhizoids  and  the  stolon  extend- 
ing from  an  older  group. 

By  this  means  the  gonidia  are  freed.     These  gonidia  germinate 
and  produce  the  mycelium  again. 

389.  Sexual  stage. — This  stage  is  not  so  frequently  found,  but  may  some- 
times be  obtained  by  growing  the  fungus  on  bread. 

Conjugation  takes  place  in  this  way.  Two  threads  of  the  mycelium  which 
lie  near  each  other  put  out  each  a  short  branch  which  is  clavate  in  form. 
The  ends  of  these  branches  meet,  and  in  each  a  septum  is  formed  which  cuts 
off  a  portion  of  the  protoplasm  in  the  end  from  that  of  the  rest  of  the  my- 
celium. The  meeting  walls  of  the  branches  now  dissolve  and  the  protoplasm 
of  each  gamete  fuses  into  one  mass.  A  thick  wall  is  now  formed  around  this 
mass,  and  the  outer  layer  becomes  rough  and  brown.  This  is  the  zygote  or 
zygospore.  The  mycelium  dies  and  it  becomes  free  often  with  the  suspensors, 
as  the  stalks  of  these  sexual  branches  are  called,  still  attached.  This  zygo- 
spore passes  through  a  period  of  rest,  when  with  the  entrance  of  favorable 
conditions  of  growth  it  germinates,  and  usually  produces  directly  a  sporan- 
gium with  gonidia.  This  completes  the  normal  life  cycle  of  the  plant. 

390.  Gemmae. — Gemmae,  as  they  are  sometimes  called,  are  often  formed  on 
the  mycelium.     A  short  cell  with  a  stout  wall  is  formed  on  the  side  of  a 


ISO  MORPHOLOGY. 

thread  of  the  mycelium.     In  other  cases  large  portions  of  the  threads  of  the 
mycelium  may  separate  into  chains  of  cells.     Both  these  kinds  of  cells  are 


Fig.  194. 

A  mucor  (Rhizopus  nigricans)  ;  at  left  nearly  mature  sporangium  with  columella  showing 
within;  in  the  middle  is  ruptured  sporangium  with  some  of  the  gonidia  clinging  to  the  colu- 
mella ;  at  right  two  ruptured  sporangia  with  everted  columella. 

capable  of  growing  and  forming  the  mycelium  again.     They  are  sometimes 
called  chlamydospores. 

390a.  The  Mucorineae  according  to  their  manner  of  zygospore  formation 
are  of  two  kinds:  ist,  the  homothallic  (monoecious),  in  which  all  of  the  colo- 
nies or  thalli  developed  from  different  spores  are  the  same,  and  both  gametes 
may  be  developed  from  the  mycelium  from  a  single  spore,  as  in  Sporodinia 
grandis,  a  mould  common  on  old  mushrooms;  2d,  the  heterothallic  (dioe- 
cious), in  which  certain  plants  are  of  a  male  nature  and  small  in  compari- 
son with  those  of  perhaps  a  female  nature  which  are  larger  or  more  vigor- 
ous. When  grown  separately  each  of  these  two  kinds  of  thalli,  or  colonies 
of  mycelium,  produce  their  own  kind  but  only  sporangia.  If  the  two  kinds 
are  brought  together,  however,  branches  from  one  conjugate  with  branches 
from  the  other  and  zygospores  are  produced,  as  in  Rhizopus  nigricans,  the 
common  bread  or  fruit  mould.  This  is  one  reason  why  we  rarely  find  this 
fungus  forming  zygospores.  (See  Blakeslee,  Sexual  Reproduction  in  the 
Mucorineae,  Proc.  Am.  Acad.  Arts  and  Sci.,  40,  205-319,  pi.  1-4,  1904.) 


FUNGI:    SAPROLEGNIA.  l8l 


Water  Moulds  (Saprolegnia). 

391.  The  water  moulds  are  very  interesting  plants  to  study 
because  they  are  so  easy  to  obtain,  and  it  is  so  easy  to  observe  a 
type  of  gonidium  here  to  which  we  have  referred  in  our  studies 
ofthealgae,  the  motile  gonidium,  or  zoogbnidium.      (See  appen- 
dix for  directions  for  cultivating  this  mould.) 

392.  Appearance  of  the  saprolegnia. — In  the  course  of  a 
few  days  we  are  quite  certain  to  see  in  some  of  the  cultures  deli- 
cate whitish  threads,  radiating  outward  from  the  body  of  the  fly 
in  the  water.      A  few  threads  should  be  examined  from  day  to 
day  to  determine  the  stage  of  the  fungus. 

393.  Sporangia  of  saprolegnia. — The  sporangia  of  saprolegnia 
can  be  easily  detected  because  they  are  much  stouter  than  the 
ordinary  threads  of  the  mycelium.     Some  of  the  threads  should 
be  mounted  in  fresh  water.     Search   for  some  of  those  which 


Fig.  795.         •;-^;i; 

Sporangia  of  saprolegnia,  one  showing  the  escape  of  the  zoogo- 
nidia. 

show  that  the  protoplasm  is  divided  up  into  a 
great  number  of  small  areas,  as  shown  in  fig.  195. 
With   the  low  power  we  should  watch  some  of  the  older  ap- 
pearing ones,  and  if  after  a  few  minutes  they  do  not  open,  other 
preparations  should  be  made. 


\ 


1 82  MORPHOLOGY. 

394.  Zoogonidia  of  saprolegnia. — The  sporangium  opens  at 


Fig.  196. 
Branch  of  saprolegtria  showing  oogonia  with  oospores,  eggs  matured  parthenogenetically. 

the  end,  and  the  zoogonidia  swirl  out  and  swim  around  for  a 
short  time,  when  they  come  to  rest.     With  a  good  magnifying 


Fig.  197-  Fig.  *98. 

Downy  mildew  of  grape  (Plasmopora  viti-  Phytophthora  infestans  showing  \,e- 

cola),  showing  tuft  ofgonidiophpres  bearing  culiar  branches ;  gonidia  below, 

gonidia,  also  intercellular  mycelium.    (After 
Millardet.) 

power  the  two  cilia  on  the  end  may  be  seen,  or  we  may  make 


FUNGI:   SAPROLEGNIA. 


Fig.  199. 

Fertilization  in  saprolegnia,  tube  of  antheridium  carrying  in  the  nucleus  of  the  sperm  ojil 
to  the  egg.  In  the  right-hand  figure  a  smaller  sperm  nucleus  is  about  to  fuse  with  the 
nucleus  of  the  egg.  (After  Humphrey  and  Trow.) 


Fig.  200. 
Branching  hypha  of  Peronospora  alsinearum. 


Fig.  aoi. 

Branched  hypha  of  downy  mildew 
of  grape  showing  peculiar  branching 
(Plasmopara  viticola). 


1 84 


MORPHOLOG  Y. 


them  more  distinct  by  treatment  with  Schultz's  solution,  draw- 
ing some  under  the  cover  glass.  The  zoogonidium  is  oval  and 
the  cilia  are  at  the  pointed  end.  After  they  have  been  at  rest 
for  some  time  they  often  slip  out  of  the  thin  wall,  and  swim 
again,  this  time  with  the  two  cilia  on  the  side,  and  then  the 
zoogonidium  is  this  time  more  or  less  bean-shaped  or  reniform. 

395.  Sexual  reproduction  of  saprolegnia. — When  such  cultures  are  older 
we  often  see  large  rounded  bodies  either  at  the  end  of  a  thread,  or  of  a 
branch,  which  contain  several  smaller  rounded  bodies  as  shown  in  fig.  196. 
These  are  the  oogonia  (unless  the  plant  is  attacked  by  a  parasite),  and  the 
round  bodies  inside  are  the  egg  cells,  if  before  fertilization,  or  the  eggs,  if 
after  this  process  has  taken  place.  Sometimes  the  slender  antheridium  can 
be  seen  coiled  partly  around  the  oogonium,  and  one  end  entering  to  come  in 
contact  with  the  egg  cell.  But  in  some  species  the  antheridium  is  not 
present,  and  that  is  the  case  with  the  species  figured  at  196.  In  this  case 


B 


Fig.  202. 


Fig.  203. 


Gonidiophores  and  gonidia  of  potato  blight  (Phytophthora  in-        Gonidia     of     potato 
festans).    6,  an  older  stage  showing  how  the  branch  enlarges  where    blight    forming    zoogo- 


it  grows  beyond  the  older  gonidutm.     (After  de  Bary.) 


nidia.     vAfter  de  Bary.) 


the  eggs  mature  without  fertilization.  This  maturity  of  the  egg  without 
fertilization  is  called  parthenogenesis,  which  occurs  in  other  plants  also,  but 
is  a  rather  rare  phenomenon.  ,;  | 

396.  In  fig.  199  is  shown  the  oogonium  and  an  antheridium,  and  the 
antheridium  is  carrying  in  the  mate  nucleus  to  the  egg  cell.  Spermatozoids 
are  not  developed  here,  but  a  nucleus  in  the  antheridium  reaches  the  egg 
cell.  It  sinks  in  the  protoplasm  of  the  egg,  comes  in  contact  with  the  nu- 
cleus of  the  egg,  and  fuses  with  it.  Thus  fertilization  is  accomplished. 


FUNGI:   DOWNY  MILDEWS.  15$ 

Downy  Mildews. 

397.  The  downy  mildews  make  up  a  group  of  plants  which  are  closely 
related  to  the  water  moulds,  but  they  are  parasitic  on  land  plants,  and  some 
species  produce  very  serious  diseases.  The  mvcelium  grows  between  the 


Fig.  204. 

Fertilization  in  Peronospora  alsinearum;  tube  from  antheridium  carrying  in  the 
sperm  nucleus  in  figure  at  the  left,  female  nucleus  near;  fusion  of  the  two  nuclei 
shown  in  the  two  other  figures.  (After  Berlese.) 

cells  of  the  leaves,  stems,  etc.,  of  their  hosts,  and  sends  haustoria  into  the 
cells  to  take  up  nutriment.  Gonidia  are  formed  on  threads  which  grow 
through  the  stomates  to  the  out- 
side and  branch  as  shown  in  figs. 
198-201.  The  gonidia  are  borne 
on  the  tips  of  the  branches.  The 
kind  of  branching  bears  some  re- 
lation to  the  different  genera. 
Fig.  200  is  from  Peronospora 
alsinearum  on  leaves  of  ceras- 
tium;  figs.  197  and  i99arePlas- 
mopara  viticola,  the  grape  mil- 
dew, while  figs.  198  and  202  are 
from  Phytophthora  infestans 
which  causes  a  disease  known  as 
potato  blight.  The  gonidia  of 
peronospora  germinate  by  a  germ 

tube,  those  of  plasmopara   first  Fig.  205. 

,  .  Ripe  oospore  of  Peronospora  alsinearum. 

form  zoogomdia,  while  in  phy- 

tophthora  the  gonidium  may  either  germinate  forming  a  thread,  or  each 
gonidium  may  first  form  several  zoogonidia,  as  shown  in  fig.  20^. 

398.  In  sexual  reproduction  oogonia  and  antheridia  are  developed  on  the 
mycelium  within  the  tissues.  Fig.  204  represents  the  antheridium  enter- 


1 86  MORPHOL  OG  Y. 

ing  the  oogonium,  and  the  male  nucleus  fusing  with  the  female  nucleus 
in  fertilization.  The  sexual  organs  of  Phytophthora  infestans  are  not 
sufficiently  known. 

399.  Mucor,  saprolegnia,  peronospora,  and  their  relatives  have  few  or 
no  septa  in  the  mycelium.  In  this  respect  they  resemble  certain  of  the  algae 
like  vaucheria,  but  they  lack  chlorophyll.  They  are  sometimes  called  the 
alga-like  fungi  and  belong  to  a  large  group  called  Phycomycetes. 


CHAPTER  XX. 


FUNGI    CONTINUED. 

"  Rusts"  (Uredineae). 

400.  The  fungi  known  as  " rusts"  are  very  important  ones 
to  study,  since  all  the  species  are  parasitic,  and  many  produce 
serious  injuries  to  crops. 

401.  Wheat  rust  (Puccinia  graminis). — The  wheat  rust   is 
one  of  the  best  known  of  these  fungi,  since  a  great  deal  of  study 
has  been  given  to  it.     One  form  of  the  plant  occurs  in  long 


Fig.  206. 

Wheat  leaf  with  red 
rust,  natural  ?ize. 


Fig.  208. 
Natural  size. 


Fig.  209. 
Enlarged. 


Fig.  207. 
Portion  of  'eaf 
enlarged  to  show 
sori. 

Figs.  206,  207. — Puccinia  graminis,  red-rust  stage  (uredo  stage). 
Figs.  208-210. — Black  rust  of  wheat,  showing  sori  of  teleutospores. 


Fig.  2 TO. 

Single 

sorus. 


reddish-brown  or  reddish  pustules,  and  is  known  as  the  "red 
rust"  (figs.  206,  207).  Another  form  occurs  in  elongated  black 
pustules,  and  this  form  is  the  ^jie  known  as  the  "black  rust** 

187 


1 88 


MORPHCLOG  V. 


(figs.   208-211).     These  two  forms  occur  on  the  stems,  blades, 
etc.,  of  the  wheat,  also  on  oats,  rye,  and  some  of  the  grasses. 

402.  Teleutospores  of  the  black-rust  form. — If  we  scrape  off 
some  portion  of  one  of  the  black  pustules  (sori),  tease  it  out 


Fig.  212. 

Teleutospores    or    wheat    rust, 
showing  two  cells  and  the  pedicel. 


,     Fig.   2TI. 

Head   of  wheat  showing  black  rust  spots 
on  the  chaff  arid  awns. 


Fig.  213. 

Uredospores  of  wheat  rust,  one 
showing  remnants  of  the  pedicel. 


in  water  on  a  slide,  and  examine  with  a  microscope,  we  see 
numerous  gonidia,  composed  of  two  cells,  and  having  thick, 
brownish  walls  as  shown  in  fig.  212.  Usually  there  is  a  slender 
brownish  stalk  on  one  end.  These  gonidia  are  called  teleuto- 
spores.  They  are  somewhat  oblong  or  elliptical,  a  little  con- 
stricted where  the  septum  separates  the  two  cells,  and  the  end 
cell  varies  from  ovate  to  rounded.  The  mycelium  of  the  fungus 


FUNGI:   RUSTS. 


I89 


courses  between  the  cells,  just  as  is  found  in  the  case  of  the 
carnation  rust,  which  belongs  to  the  same  family  (see  Parag.  186). 
403.  Uredospores  of  the  red-rust  form.— If  we  make  a  simi" 
lar  preparation  from  the  pustules  of  the  red-rust  form  we  see 
that  instead  of  two-celled  gonidia  they  are  one-celled.  The 
walls  are  thinner  and  not  so  dark  in  color,  and  they  are  covered 
with  minute  spines.  They  have  also  short  stalks,  but  these  fall 
away  very  easily.  These  one-celled  gonidia  of  the  red-rust  form 
are  called  "uredospores."  The  uredospores  and  teleutospores 
are  sometimes  found  in  the  same  pustule. 

It  was  once  supposed  that  these  two  kinds  of  gonidia  belonged 
to  different  p]ants,  but  now   it  is  known   that  the   one-celled 
form,  the  uredospores,  is  a  form  developed 
earlier  in  the  season  than  the  teleutospores. 
404.  Cluster-cup  form  on  the  barberry. 
— On    the    barberry   is    found  still  another 
form  of  the  wheat  rust,  the  ' '  cluster  cup ' ' 
stage.     The  pustules  on  the  under  side  of 
the  barberry  leaf  are  cup-shaped,  the  cups 
being  partly  sunk  in  the  tissue  of  the  leaf, 
while  the  rim  is  more  or  less  curved  back- 
ward     against 
the    leaf,    and 
split  at  several 
places.     These 
cups   occur  in 
clusters  on  the 
affected    spots 
of  the  barberry 
leaf  as   shown 
in     fig.      215. 


Fig.  214. 


Barberry  leat  with  two 
diseased  spots,  natural 
size. 

Pigs.  214-216.- 


Fig.  215. 
Single     spot 
showing     cluster 
cups  enlarged. 


Fig.  216. 
Two    cluster 
cups    more  en- 
larged/showing  Within       t  h  e 
split  margin. 
Jluster-cup  stage  of  wheat  rust.  CUpS      numbers 

of  one-celled  gonidia  (orange  in  color,  called  aecidiospores)  are 
borne  in  chains  from  short  branches  of  the  mycelium,  which 
fill  the  base  of  the  cup.  In  fact  the  wall  of  the  cup  (peridium) 


190 


MORPHOLOG  Y. 


is  formed  of  similar  rows  of  cells,  which,  instead  of  separating 
into  gonidia,  remain  united  to  form  a  wall.  These  cups  are 
usually  borne  on  the  under  side  of  the  leaf. 

405.  Spermagonia. — Upon  the  upper  side  of  the  leaves  in  the  same  spot 
occur  small,  orange-colored  pustules  which  are  flask-shaped.  They  bear 
inside,  minute,  rod-like  bodies  on  the  ends  of  slender  threads,  which  ooze 


Fig.  217. 
Section  of  an  aecidium  (cluster  cup)  from  barberry  leaf . 


(After  Marshall- Ward .) 


out  on  the  surface  of  the  leaf.  These  flask-shaped  pustules  are  called 
spermagonia,  and  the  minute  bodies  within  them  spevmatia,  since  they  were 
once  supposed  to  be  the  male  element  of  the  fungus.  Their  function  is  not 
known.  They  appear  in  the  spots  at  an  earlier  time  than  the  cluster  cups. 

406.  Hpw  the  cluster-cup  stage  was  found  to  be  a  part  of  the  wheat  rust. 
— The  cluster-cup  stage  of  the  wheat  rust  was  once  supposed  also  to  be  a  dif- 
ferent plant,  and  the  genus  was  called  (zcidium.  The  occurrence  of  wheat 
rust  in  great  abundance  on  the  leeward  side  of  affected  barberry  bushes  in 
England  suggested  to  the  farmers  that  wheat  rust  was  caused  by  barberry 
rust.  It  was  later  found  that  the  aecidiospores  of  the  barberry,  when  sown 
on  wheat,  germinate  and  the  thread  of  mycelium  enters  the  tissues  of  the 
wheat,  forming  mycelrum  between  the  cells.  This  mycelium  then  bears 
the  uredospores,  and  later  the  teleutospores. 


FUNGI:  RUSTS. 


407.   Uredospores  can  produce  successive  crops  of  uredospores. — The  uredo- 
spores  are  carried  by  the  wind  to  other  wheat  or  grass  plants,  germinate 


Fig.  218. 

Section  through  leaf  of  barberry  at  point  affected  with  the  cluster-cup  stage  of  the  wheal 
rust;  spermagonia  above,  secidia  below.     (After  Marshall-Ward.) 

form  mycelium  in  the  tissues,  and  later  the  pustules  with  a  second  crop  oi 
uredospores.     Several  successive  crops  of  uredospores  may  be  developed  in 


•ft 


B 


rig.  219. 

^.section  through  sorus  of  black  rust  of  wheat,  showing  teleutospores.     B,  mycelium 
bearing  both  teleutospores  and  uredospores.     (After  de  Bary.) 

one  season,  so  this  is  the  form  in  which  the  fungus  is  greatly  multiplied  and 
widely  distributed.    - 


192 


MORPHOLOGY. 


407a.  Teleutospores  the  last  stage  of  the  fungus  in  the  season. — The  teleu- 
tospores  are  developed  late  in  the  season,  or  late  in  the  development  of  the 

host  plant  (in  this  case  the 
wheat  is  the  host).  They 
then  rest  during  the  winter. 
In  the  spring  under  favor- 
able conditions  each  cell  of 
the  teleutospore  germi- 
nates, producing  a  short 
mycelium  called  a  promy- 
celium,  as  shown  in  figs. 
222,  223.  This  promy- 
celium  is  usually  divided 
into  four  cells.  From  each 
cell  a  short,  pointed  pro- 
cess is  formed  called  a 
'*  sterigma."  Through  this 
the  protoplasm  moves  and 
Fig.  221.  forms  a  small  gonidiumon 

Germ  tube  entering  the    ,,  ,  ,.  „    , 

af  through  a  stoma.         the  end,  sometimes  called 

a  sporidium. 

408.    How  the  fungus  gets  from  the  wheat  back  to  the  barberry.— If  these 
sporidia  from  the  teleutospores  are  carried  by  the  wind  so  that  they  lodge  on 


Germinating  uredospore  of 
wheat  rust.      (After  Marshall-      leaf  through  a  stoma 
Ward.) 


Fig.  222.  Fig.  223.  Fig.  224. 

,   Teleutospore    g  e  r  m  i  -        Promycelium    of    ger-        Germinating  sporidia  entering  leal 
nating,    forming    promy-    initiating       teleutospore,     of  barberry  by  mycelium, 
celium.  forming  sporidia. 

Figs.  222-224.— Puccinia  graminis  (wheat  rust).     (After  R4arshall-Ward.) 


•FUNGI:  XUSTS.  1 93 

the  leaves  of  the  barberry,  they  germinate  and  produce  the  cluster  cup  again. 
The  plant  has  thus  a  very  complex  life  history.  Because  of  the  presence  of 
several  different  forms  in  the  life  cyle,  it  is  called  a  polymorphic  fungus. 

The  presence  of  the  barberry  does  not  seem  necessary  in  all  cases  for  the 
development  of  the  fungus  from  one  year  to  another. 

409.  Synopsis  of  life  history  of  wheat  rust. 

Cluster -cup  stage  on  leaf  of  barberry. 

Mycelium  between  cells  of  leaf  in  affected  spots. 
Spermagonia  (sing,  spermagonium),  small  flask-shaped  bodies 

sunk  in  upper  side  of  leaf;  contain  "  spermatia. " 
^cidia  (sing,  secidium),  cup-shaped  bodies  in  under  side  of 

leaf. 
Wall  or  peridium,  made  up  of  outer  layer  of  fungus  threads 

which  are  divided  into  short  cells  but  remain  united. 
At  maturity  bursts  through  epidermis  of  leaf;  margin  of 
cup  curves  outward  and  downward  toward  surface  of  leaf. 
Central  threads  of  the  bundle  are  closely  packed,  but  free. 
Threads  divide  into  short  angular  cells  which  separate 
nnd  become  aecidiospores,  with  orange-colored  content. 
^Ecidiospores  carried  by  the  wind  to  wheat,  oats,  grasses, 
etc.     Here  they  germinate,  mycelium  enters  at  stomate, 
and  forms  mycelium  between  cells  of  the  host. 

Uredo  stage  (red  rusf)  on  wheat,  oats,  grasses,  etc. 
Mycelium  between  cells  of  host. 
Bears  uredospores  (i -celled)  in  masses  under  epidermis,  which 

is  later  ruptured  and  uredospores  set  free. 
Uredospores  carried  by  wind  to  other  individual  hosts,  and 

new  crops  of  uredospores  formed. 

Teleutospore  stage  (black  rust],  also  on  wheat,  etc. 
Mycelium  between  cells  of  host. 
Bears  teleutospores  (2 -celled)  in  masses  (sori)  under  epidermis, 

which  is  later  ruptured. 
Teleutospores  rest  during  winter.     In  spring  each  cell  germi- 

nates  and  produces  a  promycelium,  a  short  thread,  divided 

into  four  cells. 


1 94  MORPHOL  OGY. 

Promycelium  bears  four  sterigmata  and  four  gonidia  (or  spo- 
ridia),  which  in  favorable  conditions  pass  back  to  the  bar- 
berry, germinate,  the  tube  enters  between  cells  into  the 
intercellular  spaces  of  the  host  to  produce  the  cluster  cup 
again,  and  thus  the  life  cycle  is  completed. 

410.  Other  examples  of  the  rusts. — Some  of  the  rusts  do  great  injury  to 
fruit  trees  and  also  to  forest  trees.  The  "cedar  apples"  are  abnormal 
growths  on  the  leaves  and  twigs  of  the  cedar  stimulated  by  the  presence  of 
the  mycelium  of  a  rust  known  as  Gymnosporangium  macropus.  The 
teleutospores  are  two  celled  and  are  formed  in  the  tissue  of  the  "cedar 
apple"  or  gall.  The  teleutosori  are  situated  at  quite  regular  intervals  over 
the  surface  of  the  gall  at  small  circular  depressions,  and  can  be  easily  seen 
in  late  autumn  and  during  the  winter.  A  quantity  of  gelatine  is  developed 
along  with  the  teleutospores.  In  early  spring  with  the  warm,  spring  rains 
the  gelatinous  substance  accompanying  the  teleutospores  swells  greatly,  and 
causes  the  teleutospores  to  ooze  out  in  long,  dull,  orange-colored  strings, 
which  taper  gradually  to  a  slender  point  and  bristle  all  over  the  "cedar 
apple."  Here  the  teleutospores  germinate  and  produce  the  sporidia.  The 
sporidia  are  carried  to  apple  trees  where  they  infect  leaves  and  even  the 
fruit,  producing  here  the  cluster  cups.  There  are  no  uredospores. 

G.  globosum  is  another  species  forming  cedar  apples,  but  the  gelatinous 
strings  of  teleutospores  are  short  and  clavate,  and  the  cluster  cups  are 
formed  on  hawthorns.  G.  nidusavis  forms  "witches  brooms"  or  "birds 
nests"  in  the  branches  of  the  cedar.  The  mycelium  in  the  branches  stimu- 
lates them  to  profuse  branching  so  that  numerous  small  branches  are  devel- 
oped close  together.  The  teleutosori  form  small  pustules  scattered  over  the 
branches.  G.  clavipes  affects  the  branches  of  cedar  only  slightly  deform- 
ing them  or  not  at  all,  and  the  cluster  cups  are  formed  en  fruits,  twigs,  and 
leaves  of  the  hawthorns  or  quinces,  the  cluster  cups  being  long,  tubular, 
and  orange  in  color. 


CHAPTER  XXI. 

THE    HIGHER    FUNGI. 

411.  The  series  of  the  higher  fungi, — Of  these  there  are  two 
large  series.     One  of  these  is  represented  by  the  sac  fungi,  and 
the  other  by  the    mushrooms,  a   good  example  of  which  is  the 
common  mushroom  (Agaricus  campestris). 

Sac  Fungi   (Ascomycetes). 

412.  The  sac  fungi  may  be  represented  by  the  "  powdery  mil- 
dews";    examples,    uncinula.     microsphaera,     podosphaera,    etc. 
Fig.  225  is  from  a  photograph  of  two  willow  leaves  affected  by 
one  of  these  mildews.     The  leaves  are  first  partly  covered  with  a 
whitish  growth  of  mycelium,  and  numerous  chains  of  colorless 
gonidia  are  borne  on  short  erect  threads.     The  masses  of  gonidia 
give  the  leaf  a  powdery  appearance.     The  mycelium  lives  on  the 
outer  surface  of  the  leaf,  but  sends  short  haustoria  into  the  epi- 
dermal cells. 

413.  Fruit  bodies  of  the  willow  mildew. — On  this  same  myce- 
lium there    appear  later  numerous  black  specks  scattered  over 
the  affected  places  of  the  leaf.     These  are  the  fruit  bodies  (per- 
ithecid).     If  we  scrape  some  of  these  from  the  leaf,  and  mount 
them  in  water  for  microscopic  examination,  we  shall  be  able  to 
see  their  structure.     Examining  these  first  with  a  low  power  of 
the  microscope,  each  one  is  seen  to  be  a  rounded  body,  from 
which  radiate  numerous  filaments,  the  appendages.     Each  one 
of  these  appendages  is  coiled  at  the  end  into  the  form  of  a  little 
hook.     Because  of  these  hooked  appendages  this  genus  is  called 
uncinula.     This  rounded  body  is  the  perithecium. 


196 


MORPHOLOG  Y. 


414.  Asci  and  ascospores. — While  we  are  looking  at  a  few  of 
these  through  the  microscope  with  the  low  power,  we  should 


Fig.  225. 

Leaves  of  willow  showing  willow  mildew.     The  black  dots  are  the  fruit  bodies  (perithecia) 
seated  on  the  white  mycelium. 

press  on  the  cover  glass  with  a  needle  until  we  see  a  few  of  the 
perithecia  rupture.  If  this  is  done  carefully  we  see  several 
small  ovate  sacs  issue,  each  containing  a  number  of  spores,  as 
shown  in  fig.  227.  Such  a  sac  is  an  ascus,  and  the  spores  are 
ascospores. 


FUNGI:    SAC  FUNGI. 


197 


415.  Number  of  spores  in  an  ascus. — The  ascus  is  the  most  important 
character  showing  the  general  relationship  of  the  members  of  the  sac  fungi. 


Fig.  226. 


Fig.  227. 


Willow    mildew;    Fruit  of  willow  mildew,  showing  hooked 


bit  of  mycelium 
with  erect  conidio- 

chaSSfofbffonidU?    ciumV.of  two  powdery  mildews,  showing 
>ni(?la>    escape  of  asci  containing  the  spores  from 


appendages.     Genus  uncinula. 
228.— 


Fig.  228. 
Fruit  body  of  an- 
other  mildew  with 
dichotomous  _    ap- 


gonidium     at     left 
germinating. 


the  crushed  fruit  bodies. 


While  many  of  the  powdery  mildews  have  a  variable  number  of  spores  in 


Fig.  229.  Fig.  230. 

Contact      of  Disappear- 

antheridium  ance  of  contact 

and      carpogo-  walls  of  anthe- 

nium  (carpogo-  ridium     and 

nium  the  larger  carpogon ium , 

cell);     begin-  and    fusion     of 

ning  of  fertili-  the  two  nuclei, 
zation. 
Figs.  229-231. — Fertilization  in  spha? 


Fig.  231. 

Fertilized    egg    surrounded 
by    the     enveloping    threads 
which  grow  up  around  it. 
theca;   one  of  the  powdery  mildews.     (After 


Harper.) 


an  ascus,   a 


large  majority  of  the  ascomycetes  have  just  8  spores  in  an 


198 


MORPHOLOG  y. 


ascus,  while  some  have  4.  others  16,  and  some  an  indefinite  number. 
The  asci  in  a  perithecium  are  more  variable.  In  some  ascomycetes  there 
is  no  perithecium. 

416.  The  black  fungi. — These  are  very  a>/nmon  on  dead  logs,  branches, 


Fig.  2310. 

Edible  Morel.     Morchella  esculenta.     The  asci,  forming  hymenium,  cover  the 
pitted  surface. 


leaves,  etc.,  and  may  be  collected  in  the  woods  at  almost  any  season.     The 
perithecia  are  often  numerous,  scattered  or  densely  crowded  as  in  Rosel- 


FUNGI:   MUSHROOMS.  199 

linia.  Sometimes  they  are  united  to  form  a  crust  which  is  partly  formed 
from  sterile  elements  as  in  Hypoxylon,  or  they  form  black  clavate  or 
branched  bodies  as  in  Xylaria.  The  black  knot  of  the  plum  and  cherry  is 
also  an  example. 

The  lichens  are  mostly  ascomycetes  like  the  black  fungi  or  cup  fungi, 
while  a  few  are  basidiomycetes. 

417.  The   morels    (Morchella). — There    are    several    species   of   morels 
which  are  common  in  early  spring  on  damp  ground.      Either  one  of  the 
species  is  suitable  for  use  if  it  is  desired  to  include  this  in  the  study.     Fig. 
23 1 a   illustrates   the   Morchella   esculenta.      The   stem   is   cylindrical   and 
stout.     The   fruiting  portion  forms  the  "head,"  and  it    is  deeply  pitted. 
The  entire  pitted  surface  is  covered  by  the  asci,  which  are  cylindrical  and 
eight  spored.     A  thin  section  may  be  made  of  a  portion   for  study,  or  a 
small  piece  may  be  crushed  under  the  cover  glass. 

418.  The  cup  fungi. — These  fungi  are  common  on  damp   ground  or  on 
rotting  logs  in  the  summer.     They  may  be  preserved  in  70  per  cent  alcohol 
for  study.     Many  of  them  are  shaped  like  broad  open  cups  or   saucers. 
The  inner  surface  of  the  cup  is  the  fruiting  surface,  and  is  covered  with  the 
cylindrical  asci,  which  stand  side  by  side.     A  bit  of  the  cup  may  be  sec- 
tioned or  crushed  under  a  cover  glass  for  study. 

Mushrooms  (Basidiomycetes). 

419.  The  large  group  of  fungi  to  which  the  mushroom  belongs  is  called 
the  basidiomycetes  because  in  all  of  them  a  structure  resembling   a  club, 
or  basidium,  is  present,  and  bears  a  limited  number  of  spores,  usually  four, 
though  in  some  genera   the   number  is  variable.      Some  place  the  rusts 
(Uredineae)  in  the  same  series  (basidium  series),  because  of  the  short  pro- 
mycelium  and  four  sporidia  developed  from  each  cell  of  the  teleutospore. 

420.  The  gill-bearing  fungi  (Agaricaceae). — A  good  example 
for  this  study  is  the  common  mushroom  (Agaricus  campestris). 

This  occurs  from  July  to  November  in  lawns  and  grassy  fields. 
The  plant  is  somewhat  umbrella-shaped,  as  shown  in  fig.  232, 
and  possesses  a  cylindrical  stem  attached  to  the  under  side  of  the 
convex  cap  or  pileus.  On  the  under  side  of  the  pileus  are  thin 
radiating  plates,  shaped  somewhat  like  a  knife  blade.  These  are 
the  gills,  or  lamellae,  and  toward  the  stem  they  are  rounded  on 
the  lower  angle  and  are  not  attached  to  the  stem.  The  longer 
ones  extend  from  near  the  stem  to  the  margin  of  the  pileus,  and 
the  V-shaped  spaces  between  them  are  occupied  by  successively 


200 


MORPHOLOG  Y. 


Fig.  232. 
Agaricus  campestris.     View  of  under  side  showing  stem,  annulus,  gills,  and  margin  of  pileus. 


Fig. 233- 

Agaricus  campestris.     Longitudinal  section  through  stem  and  pileus.    a,  pileus;  6,  portion 
of  veil  on  margin  of  pileus  ;  c,  gill ;  ft  fragment  of  aunulus  ;  e,  stipe. 


FUNGI:    MUSHROOMS. 


201 


shorter  ones.    Around  the  stem  a  little  below  the  gills  is  a  collar, 
termed  the  ring  or  annulus. 

421.  Fruiting  surface  of  the  mushroom. — The  surface  of 
these  gills  is  the  fruiting  surface  of  the  mushroom,  and  bears  the 
gonidia  of  the  mushroom,  which  are  dark  purplish  brown  when 
mature,  and  thus  the  gills  when  old  are  dark  in  color.  If  we  make 
a  thin  section  across  a  few  of  the  gills,  we  see  that  each  side  of 
the  gill  is  covered  with  closely  crowded  club-shaped  bodies,  each 
one  of  which  is  a  basidium.  In  fig.  234  a  few  of  these  are  en- 
larged, so  that  the 
structure  of  the  gill 
can  be  seen.  Each 
basidium  of  the  com- 


Fig.  234- 

Portion  of  section  of  lamella  of  Agaricus  campestris. 
tr,  trama ;  sk,  subhymenium ;  b,  basidium;  st,  sterigma 
( //.  sterigmata) ;  g,  ba'sidiospore. 


-  235. 

Portion  of  hymenium  of  Co- 
prinus  micaceus,  showing  large 
cystidium  in  the  hymenium. 


two  spinous  processes  at  the  free  end.  Each  one  is  a  sterig'ma 
(plural  sterig' mata},  and  bears  a  gonidium.  In  a  majority  of  the 
members  of  the  mushroom  family  each  basidium  bears  four 
spores.  When  mature  these  spores  easily  fall  away,  and  a  mass 
of  them  gives  a  purplish-black  color  to  objects  on  which  they  fall, 
so  that  a  print  of  the  under  surface  of  the  cap  showing  the 
arrangement  of  the  gills  can  be  obtained  by  cutting  off  the  stem, 
and  placing  the  pileus  on  white  paper  for  a  time. 

422.  How  the  mushroom  is  formed. — The  mycelium  of  the 


202 


MORPHOLOGY. 


FUNGI:    MUSHROOMS  2O3 

mushroom  lives  in  the  ground,  and  grows  here  for  several  months 
or  even  years,  and  at  the  proper  seasons  develops  the  mature 
mushroom  plant.  The  mycelium  lives  on  decaying  organic  mat- 
ter, and  a  large  number  of  the  threads  grow  closely  together  form- 
ing strands,  or  cords,  of  mycelium,  which  are  quite  prominent 
if  they  are  uncovered  by  removing  the  soil,  as  shown  in  fig.  236. 
423.  From  these  strands  the  buttons  arise  by  numerous  threads 
growing  side  by  side  in  a  vertical  direction,  each  thread  growing 
independently  at  the  end,  but  all  lying  very  closely  side  by 


Fig.  237. 

Agaricus  campestris ;  sections  of  "buttons"  of  different  sizes,  showing  formation  of  gills 
and  veil  covering  them. 

side.  When  the  buttons  are  quite  small  the  gills  begin  to 
form  on  the  inside  of  the  under  margin  of  the  knob.  They 
are  formed  from  an  interior  ring  of  tissue  near  the  end  of  the 
young  fruit  body  which  appears  before  the  end  broadens  into 
a  knob.  From  this  ring  of  tissue  threads  grow  downward  in 
radiating  ridges,  just  as  many  ridges  being  started  as  there 
are  to  be  gills  formed.  The  lateral  tissue  outside  of  this  in- 
terior ring  of  gills  becomes  the  veil,  and  sections  oi  young  but- 
tons will  disclose  the  gills  in  the  minute  cavity  thus'  forme~d 
(fig.  237).  This  curtain  of  mycelium  which  is  thus  stretched 
across  the  gill  cavity  is  the  veil.  As  the  cap  expands  more 
and  more  this  is  stretched  into  a  thin  and  delicate  texture  as 


204  'MOKPHOLOG  Y. 

shown  in  fig.  238.     Finally,  as  shown  in  fig.  239,  this  veil  is 
ruptured  by  the  expansion  of  the   pileus,  and  it  either  clings 


Fig.  238. 

Agaricus  campestris  ;     nearly  mature  plants,  showing  veil  still  stretched  across  the  giH 
cavity. 


Fig.  239. 

Agaricus  campestris  ;  under  view  of  two  plants  just  after  rupture  of  veil,  fragments  of  the 
latter  clinging  both  to  margin  of  pileus  and  to  stem. 


FUNGI:   MUSHROOMS. 


205 


Fig.  240. 

Agaricus  campestris  ;  plant  in  natural  position  just  after  rupture  of  veil,  showing  tendencj 
to  double  annulus  on  the  stem.     Portions  of  the  veil  also  dripping  from  margin  of  pileus. 


Fig.  241. 
Agaricus  campestns ;  spore  print. 


206 


MORPHOLOGY. 


sr  hj 
•Ss 

s 

SI 


FUNGI:    MUSHROOMS.  2O/ 

to  the  stem  as  a  collar,  or  a  portion  of  it  remains  clinging  to 
the  margin  of  the  cap.  When  the  buttons  are  very  young 
the  gills  are  white,  but  they  soon  become  pink  in  color,  and 


Fig.  243. 
Amanita  phalloides ;  white  form,  showing  pileus,  stipe,  annulus,  and  volva, 

very  soon  after  the  veil  breaks  the    spores    mature,    and    then 
the  gills  are  dark  brown. 

424.  Beware  of  the  poisonous  mushroom. — The  number  of 
species  of  mushrooms,  or  toadstools  as  they  are  often  called,  is 
very  great.  Besides  the  common  mushroom  (Agaricus  campes- 


208 


MORPHOLOG  Y. 


tris)  there  are  a  large  number  of  other  edible  species.  But 
one  should  be  very  familiar  with  any  species  which  is  gathered 
for  food,  unless  collected  by  one  who  certainly  knows  what  the 
plant  is,  since  carelessness  in  this  respect  sometimes  results  fatally 
from  eating  poisonous  ones. 

425.  A  plant  very  similar  in  structure  to  the  Agaricus  campes- 
tris  is  the  Lepiota  naucina,  but  the  spores  are  white,  and  thus  the 
gills  are  white,  except  that  in  age  they  become  a  dirty  pink. 
This  plant  occurs  in  grassy  fields  and  lawns  often  along  with  the 


Fig.  244. 

Arnanita  phalloides  ;  plant  turned  to  one  side,  after  having  been  placed  in  a  horizontal 
position,  by  the  directive  force  of  gravity. 


common  mushroom.  Great  care  should  be  exercised  in  collect- 
ing and  noting  the  characters  of  these  plants,  for  a  very  deadly 
poisonous  species,  the  deadly  amanita  (Amanita  phalloides)  is 
perfectly  white,  has  white  spores,  a  ring,  and  grows  usually  in 
wooded  places,  but  also  sometimes  occurs  in  the  margins  of  lawns. 
In  this  plant  the  base  of  the  stem  is  seated  in  a  cup-shaped  struc- 
ture, the  volva,  shown  in  fig.  243.  One  should  dig  up  the  stem 
carefully  so  as  not  to  tear  off  this  volva  if  it  is  present,  for  with 
the  absence  of  this  structure  the  plant  might  easily  be  mistaken 
for  the  lepiota,  and  serious  consequences  would  result. 


FUNGI:   MUSHROOMS.  209 

426.  Tube-bearing  fungi  (Polyporaceae). — In  the  tube-bearing  fungi,  the 
fruiting  surface,  instead  of  lying  over  the  surface  of  gills,  lines  the  surface 
of  tubes  or  pores  on  the  under  side  of  the  cap.  The  fruit-bearing  portion 
therefore  is  "honey-combed."  The  sulphur  polyporus  (Polyporus  sulphu- 
reus)  illustrates  one  form.  The  tube-bearing  fungi  are  sometimes  called 
"bracket"  fungi,  or  "shelf"  fungi,  because  the  pileus  is  attached  to  the 


Fig.  245. 

Edible    Boletus.     Boletus   edulis.     Fruiting   surface    honey-combed    on    under 
side  of  cap. 

tree  or  stump  like  a  shelf  or  bracket.  One  very  common  form  in  the  woods 
is  the  plant  so  much  sought  by  "artists,"  and  often  called  Polyporus  ap- 
planatus.  It  is  hard  and  woody,  reddish  brown,  brown  or  grayish  on  the 
upper  side,  according  to  age,  and  is  marked  by  prominent  and  large  concentric 
ridges.  (This  form  is  probably  P.  leucophaeus.)  The  under  side  is  white 
and  honey-combed  by  numerous  very  minute  pores.  This  plant  is  peren- 
nial, that  is,  it  lives  from  year  to  year.  Each  year  a  new  layer  is  added  to 
the  under  side,  and  several  new  rings  usually  to  the  margin.  If  a  plant 
two  or  three  years  old  is  cut  in  two,  there  will  be  seen  several  distinct  tube 
layers  or  strata,  each  one  representing  a  year's  growth. 

In  some  of  these  bracket  fungi,  each  ring  on  the  upper  surface  marks  a 


2 1 0  MORPHOL  OGY. 

year's  growth  as  in  the  pine  polyporus  (P.  pi ni cola).  In  the  birch  poly- 
porus  (P.  fomentarius)  the  tubes  are  quite  large.  It  also  occurs  on  other 
trees.  The  beech  polyporus  (P.  igniarius,  also  on  other  trees)  often  be- 


Fig.  246. 
Coral  fungus.      Hydnum  coralloides,  spines  hanging  down  from  branches. 

comes  very  old.  I  have  seen  one  specimen  over  eighty  years  old.  Not  all 
the  tube-bearing  fungi  are  bracket  form.  Some  have  a  stem  and  cap 
(see  fig.  245).  Some  are  spread  on  the  surface  of  logs. 

427.  Hedgehog  fungi  (Hydnaceae). — These  plants  are  bracket  in  form  or 
have  a  stem  and  cap,  or  are  spread  on  the  surface  of  wood;   but  the  finest 
specimens  resemble  coral  masses  of  fungus  tissue    (example,  Hydnum,  fig. 
246).      In  most  of  them  there  are  slender  processes  resembling  teeth,  spines 
or  awls,  which  depend  from   the   under  surface  (fig.  247).     The   fruiting 
surface  covers  these  spines. 

428.  Coral  fungi   or   fairy   clubs     (Clavariaceae). — These  plants   stand 
upright  from  the  wood,   leaves,  or  soil,   on  which  they   grow  (example, 
Clavaria).     The  "coral"  ones  are  branched,  while  the  "fairy  clubs"  are 
simple.      The  fruiting  surface  covers  the  entire  exposed  surface  of  the  plants 
(fig.  248). 


FUNGI:   MUSHKOOMS. 


Fig.  247. 
Hydnum  repandum,  spines  hanging  down  from  under  side  of  cap. 


212  MORPHOLOGY. 


Fig.  248. 
Clavaria  botrytes. 


CHAPTER   XXII. 


CLASSIFICATION    OF   THE    FUNGI. 

429.  Classification  of  the  fungi. — Those  who  believe  that  the  fungi  repre- 
sent a  natural  group  of  plants  arrange  them  in  three  large  series  related  to 
each  other  somewhat  as  follows'. 

The  Basidium  Type  or  Series. 
The  number  of  gonidia  on  a  ba- 
sidium  is  limited  and  definite, 
and  the  basidium  is  a  characteris- 
tic structure;  examples:  uredineae 
(rusts),  mushrooms,  etc. 

The  Ascus  Type  or  Series.  The 
number  of  spores  in  an  ascus  is 
limited  and  definite,  and  the  ascus  is 
a  characteristic  structure;  examples: 
leaf  curl  of  peach  (exoascus),  pow- 
dery mildews,  black  knot  of  plum, 
black  rot  of  grapes,  etc. 

430.  Others  believe  that  the  fungi  do  not  represent  a  natural  group,  but 
that  they  have  developed  off  from  different  groups  of  the  algae  by  becoming 
parasitic.      As  parasites  they  no  longer  needed  chlorophyll,   and  conse- 
quently lost  it. 

According  to  this  view  the  lower  fungi  have  developed  off  from  the  lower 
algae  (saprolegnias,  mucors,  peronosporas,  etc.,  being  developed  off  from 
siphonaceous  algae  like  vaucheria),  and  the  higher  fungi  being  developed 
off  from  the  higher  algae  (the  ascomycetes  perhaps  from  the  Rhodophyceae) . 

431.  A  very  general  outline  of  classification,*  according  to  the  former  of 


The  Gonidium  Type  or  Series. 
The  number  of  gonidia  in  the  spo- 
rangium is  indefinite  and  variable. 
It  may  be  very  large  or  very  small, 
or  even  only  one  in  a  sporangium. 
To  this  series  belong  the  lower 
fungi;  examples:  mucor,  saprolegnia, 
peronospora,  etc. 


*  Class  Myxomycetes,  or  Mycetozoa.  —  To  this  class  belong  the  "slime 
molds,"  low  organisms  consisting  of  masses  of  naked  protoplasm  which 
flows  among  decaying  leaves  and  in  decaying  wood,  coming  to  the  surface 
to  fruit.  The  fruit  in  many  cases  resembles  miniature  puff-balls,  and  these 
plants  were  formerly  classed  with  the  puff-balls.  The  spores  germinate  by 

213 


214 


MORPHOLOG  Y. 


these  views,  might  be  presented  here  to  show  the  general  relationships  of 
the  fungi  studied,  with  the  addition  of  a  few  more  in  orders  not  represented 
above.  It  should  be  borne  in  mind  that  the  author  in  presenting  this  view 
of  classification  does  not  necessarily  commit  himself  to  it.  It  is  based 
on  that  presented  in  Engler  &  Prantl's  Pflanzenfamilien.  There  are  three 
classes. 

I.  Class  Phycomycetes  (Alga-like  Fungi). 

1.  SUBCLASS  OOMYCETES. 

432.  These   are   the   egg-spore   fungi.     They   include   the   water   mold 
(Saprolegnia),  the  downy  mildew  of  the  grape  (Plasmopara),  the  potato 


B 

Fig.  249. 

Chytrids.  A,  Harpochytrium  hedenii,  parasitic  on  spirogyra  threads;  a,  sickle, 
form  plant;  b,  the  sporangium  part  with  escaping  zoospores;  c,  old  plant  pro- 
liferating by  forming  new  sporangium  in  the  old  empty  one;  d,  zoospore;  e,  two 
young  plants  just  beginning  to  grow.  B,  Rhizophidium  globosum  parasitic  on 
spirogyra.  Globose  sporangium  with  delicate  threads  inside  of  the  host,  zoospores 
escaping  from  one.  C,  Olpidium  pendulum,  parasitic  in  spirogyra  cell.  Ellip- 
tical sporangium  with  slender  exit  tube  through  which  zoospores  are  escaping. 
Df  Lagenidium  rabenhorstii  parasitic  in  spirogyra  cell.  Two  slender  sporangia 
with  exit  tubes  through  which  protoplasm  escapes  forming  a  rounded  mass  at  the 
end  of  tube,  this  protoplasm  forming  biciliate  zoospores. 


forming  swarm  spores  which  unite  to  form  a  small  plasmodium,  which  in 
turn  grows  to  form  a  large  plasmodium  or  protoplasmic  mass.  It  is  doubt- 
ful if  they  are  any  more  plant  than  animal  organisms.  Examples:  Trichia, 
Arcyria,  Stemonitis,  Physarum,  Ceratiomyxa,  etc.,  on  rotten  wood;  Plas- 
modiophora  brassicae  is  a  parasite  causing  club  foot  of  cabbage,  radishes, 
etc.  It  lives  within  the  roots,  causing  large  knots  and  swellings  on  the  same. 


FUNGI  CONTINUED:    CLASSIFICATION. 


215 


blight  (Phytophthora),  the  white  rust  of  cruciferous  plants  (Cystopus  = 
Albugo),  the  damping-off  fungus  (Pythium),  and  many  parasite%  of  the 
dlgse  known  as  chytrids,  as  Olpidium,  Rhizophidium,  Lagenidium,  Chytri- 
dium,  etc. 

The  two  following  orders  are  sometimes  placed  in  a  separate  subclass, 
A  rchimycetes. 

433.  Order  Chytridiales  (Chytridineae). — These  include  the  lowest  fungi. 
Many  of  them  are  parasitic  on  algas  and  lack  mycelium,  the  swarm  spore 
either  with  or  without  minute  rhizoids,  developing  into  a  globose  sporan- 
gium (Rhizophidium,  Chytridium,  Olpidium,  etc.,  fig.  249),  or  the  swarm 
spore  attached  to  the  wall  of  the  host  develops  into  a  long  sword-shaped 
body  with  a  sterile  base,  which  proliferates  ..-••.•>;. 

and  forms  a  new  sporangium  in  the  old  one 
(Harpochytrium),  or  with  slight  develop- 
ment of  mycelium  in  aquatic  plants  (Cla- 
dochytrium).  Some  are  parasitic  in  leaves 
and  stems  of  land  plants.  Synchytrium 
decipiens  is  very  common  on  the  trailing 
legume,  Amphicarpaea  monoica. 

434.  Order  Ancylistales  (Ancylistineae). 
— The  members  of  this  order  have  a  slight 
development    of    mycelium  and  many  are 
parasitic  in  algae  (Lagenidium,  fig.  249). 

435.  Order    Saprolegniales     (Saproleg- 
niineae). — These  include  the  water  molds 
(Saprolegnia).     See  Chapter  XIX. 

436.  Order    Monoblepharidales    (Mono- 
blepharidineae). — These  are  peculiar  water 
molds,  related   to    the   Saprolegniales,  but 
motile  sperm  cells   are  formed  (Monoble- 

pharis,  etc.,  fig.  250).  Fig.  250. 

437.  Order  Peronosporales  (Peronospori-    .   Monoblepharis    insignis  Thax- 

ter.      hnd  of  nypha  bearing  oo<?  .- 

neae). — These  include  the  downy  mildews  nium  (oog)  and  antheridium  d.nt) 
/T>  Sperms  escaping  from  antheridium 

(Peronospora,    Plasmopara,    Phytopthora,    and  creeping  up  on  the  oogonium. 

etc.),  and  the  white  rust  of  crucifers  and    (A£ter  Thaxter-> 
other  plants  (Cystopus=  Albugo),  Chapter  XIX. 

2.  SUBCLASS  ZYGOMYCETES. 

438.  These  are  the  conjugating  fungi. 

439.  Order  Mucorales   (Mucorineae).— This  includes  the  black  mold  and 
its  many  relatives  (Mucor,  Rhizopus,  etc.).     Chapter  XIX. 

440.  Order    Entomophthorales    (Entomophthorineae). — This    order    in- 
cludes the  "fly  fungus"  (Empusa)  and  its  many  relatives  parasitic  on  insects. 


216 


MORPHOLOGY. 


In  the  autumn  and  winter  dead  flies  are  often  found  stuck  to  window-panes, 
with  a  white  ring  of  the  conidia  around  each  fly. 

II.  Class  Ascomycetes.    (The  ascus  series.) 

1.  SUBCLASS   HEMIASCOMYCETES. 

441.  Order  Hemiascales  (Hemiascinege). — Fungi  with  a  well  developed, 

septate    mycelium,    but 
with  a  sporangium-like 
a  large  and 
number     of 


ascus,  i.e. 
indefinite 

spores  in  the  ascus.  Ex- 
amples  :  Protomyces^ 
macrosporus  in  stems  of 
Umbelliferae,  or  P.  poly- 
sporus  in  Ambrosia  tri- 
fida.  These  two  are  by. 
some  placed  in  the  Usti- 
lagineae.  Dipodascus- 
albidus  grows  in  the 
exuding  sap  of  Bromeli- 
aceae  in  Brazil  and  the 
sap  of  the  beech  in 
Sweden.  The  ascus  is 
developed  as  the  result 
of  the  fertilization  of  an 
ascogonium  with  an  an- 
theridium  (see  fig.  251). 

2.  SUBCLASS 
PEOTOASCOMYCETES. 

442.  The  a sci  are  well 

p-     2SI  defined  and  usually  with 

Dipodascus  albidus.  A,  thread  with  sexual  organs,  a  limited  and  definite 
ascogonium  and  antheridium;  B,  fertilized  ascogonium  ,-^y™.  „*  c™,-^  flicil 

developing  ascus;    C,  ascus  with  spores;    D,  conidia.  number  of    spores  (USU- 

( After  Lagerheim.)  ally   g^    sometimes   I,  2, 

4,  1 6,  or  more).     Mycelium  often  well  developed  and  septate.     Asci  scat- 
tered on  the  mycelium,  not  associated  in  definite  fields  or  groups. 

443.  Order  Protoascales  (Protoascinese) . — The  asci  are  separate  cells, 
or  are  scattered  irregularly  in  loose  wefts  of  mycelium.  No  fruit  body. 
(The  yeast,  Saccharomyces,  see  paragraph  237;  and  certain  mold-like 
fungi,  some  of  which  are  parasitic  on  mushrooms,  as  Endomyces,  are 
examples.) 


a  scoff 


FUNGI  CONTINUED:    CLASSIFICATION. 


3.  SUBCLASS  EUASCOMYCETES. 

Asci  associated  in  surfaces  forming  a  hymenium,  or  in  groups  or  inter- 
mingled in  the  elements  of  a  fruit  body.  Fruit  body  usually  present. 

The  following  four  or  five  orders  comprise  the  Discomycetes,  according 
to  the  usual  classification. 

444.  Order  Protodiscales  (Protodiscineee). —  The   asci   are   exposed  and 
form  large  and  indefinite  groups,  but  there  is  no  definite  fruit  body.     Ex- 
amples: leaf  curl  of  peach,  plum  pocket,  etc.  (Exoascus). 

445.  Order  Helvellales  (Helvellineae). — The  asci  form  large  fields  over 
the  upper  portion  of  the  fruit  body.     This  order  includes  the  morels  (fig. 
23ia),  helvellas,  earth  tongues  (Geoglossum),  etc. 

446.  Order  Pezizales   (Pezizineae).— The  asci   form   a   definite   field   or 
fruiting  surface  surrounded  on  the  sides  and  below  by  a  wall  of  fungus  tis- 
sue, forming  a  fruit  body  in  the  shape  of  a  cup.     These  are  known  as  the 
cup  fungi  (Peziza,  Lachnea,  etc.). 

447.  Ord?r  Phacidiales  (Phacidiineae). — Fungi  mostly  saprophytic,  and 
fruit  body  similar  to  the  cup  fungi.     Examples:  Propolis  in  rotting  wood, 
Rhytisma  forming  black   crusts   on    leaves    (maple   for   example),  Urnula 
craterium,  a  large  black  beaker-shaped  fungus  on  the  ground. 

448.  Order  Hysteriales  (Hysteriineae). — Fungi  with  a  more  or  less  elon- 
gated fruit  body  with  an  enclosing  wall  opening  by  a  long  slit.  "  In  some 
forms  the  fruit  body  has  the  appearance  of  a  two-lipped  body;    in  others 
it  is  shaped  like  a  clam  shell,  the  asci  being  inside.     Example,  Hystero- 
graphium  common  on  dry,  dead,  decorticated  sticks. 

449.  Order  Tuberales  (Tuberineae). — The   more   or  less  rounded  fruit 
bodies  are  usually  subterranean.     The  most  important  fungi  in  this  order 
are  the  truffles  (Tuber).     The  mycelium  of  many  species  assists  in  the 
formation  of  mycorhiza  on  the  roots  of  oaks,  etc.,  and  several  species  are 
partly  cultivated,  or  protected,  and  collected  for  food.     This  is  especially 
the  case  with  Tuber  brumale  and  its  forms;    more  than  a  million  francs 
worth  of  truffles  are  sold  in  France  and  Italy  yearly.     Dogs  and  pigs  are 
employed  in  the  collection  of  truffles  from  the  ground. 

450.  Order  Plectascales  (Plectascineae). — The  fruit  body  of  these  plants 
is  more  or  less  globose,  and  contains  the  asci  distributed  irregularly  through 
the   mycelium   of  the   interior.     Some   are   subterranean    (Elaphomyces), 
while  others  grow  in  decaying  plants,  or  certain  food  substances  (Euro- 
tium,    Sterigmatocystis,   Peniciltfum).     Penicillium    in    its    conidial    stage 
forms  blue  mold  on  fruit,  bread,  etc. 

The  following  four  orders  comprise  the  Pyrenomycetes,  according  to  the 
usual  classification. 

451.  Order  Perisporiales. — The  powdery  mildews  are  good  examples  of 
this  order  (Uncinula,  Microsphsera,  etc.,  Chapter  XXI). 


218  MORPHOLOGY. 

452.  Order    Hypocreales.* — The   fruit   bodies   are   colorless,   or  bright 
colored  and  entirely  enclose  the  asci,  sometimes  opening  by  an  apical  pore. 
Nectria  cinnabarina  has  clusters  of  minute  orange  oval  fruit  bodies,  and  is 
common  on  dead  twigs.     Cordyceps  with  a  number  of  species  is  parasitic 
on  insects,  and  on  certain  subterranean  Ascomycetes,  especially  Elapho- 
myces  (of  the  order  Plectascales=  Plectascinea) . 

453.  Order  Dothidiales.* — Fungi  with  black  stroma  formed  of  mycelium 
in  which  are  cavities  containing  the  asci.     The  cavities  are  usually  shaped 
like  a  perithecium,  but  there  is  no  wall  distinct  from  the  tissue  of  the  stroma 
(Dothidea,  Phyllachora,  on  grasses). 

454.  Order  Sphseriales.* — These  contain  the  so-called  black  fungi,  with* 
separate  or  clustered,  oval,  fiu;*"  Bodies,  black  in  color.     The  black  wall 
encloses  the  asci,   and  usually  opens  by  an  apical  pore.     Examples  ar» 
found  in  the  black  knot  of  plum  and  cherry,  black  rot  of  grapes,  and  in 
Rosellinia,  Hypoxylon,  Xylaria,  etc.,  on  dead  wood. 

455.  Order   Laboulbeniales  (Laboulbineae). — These  are  peculiar  fungi 
attached  to  the  legs  and  bodies  of  insects  by  a  short  stalk,  and  provided 
with  a  sac-like  fruit  body  which  contains  the  asci.     Example,  Laboulbenia. 

III.  Class  Basidiomycetes.    (The  basidium  series,) 

1.  SUBCLASS  HEMIBASIDIOMYCETES. 

456.  Order  Ustilaginales  (Ustilagineae). — This  order  includes  the  well- 
known  smuts  on  corn,  wheat,  oats,  etc.  (Ustilago,  Tilletia,  etc.). 

2.  SUBCLASS   JECIDIOMYCETES. 

457.  Order  Uredinales  f  (Uredinese). — This  order  includes  the  parasitic 
fungi  known  as  rusts.      Examples:   wheat  rust  (Chapter  XX),  the  cedar 
apple,  etc. 

The  true  Basidiomycetes  include  the  following  orders: 

3.  SUBCLASS   PROTOBASIDIOMYCETES. 

458.  Order   Auriculariales.f — This  order  includes   trembling    fungi    in 
which  the  basidium  is  long  and  divided  transversely  into  usually  four  cells 
(example,  Auricularia) ,  and  similar  forms.     Pilacre  petersii  on  dead  wood 
represents  an  angiocarpous  form. 

4.59.  Order   Tremellale3    (Tremellineae),    trembling    or   gelatinous    fungi 
with  the  globose  basidium  divided  longitudinally  into  four  cells  (Tremella) . 


*  As  suborder  in  Engler  and  Prantl. 

t  The  Uredinales  and  Auriculariales  in  Engler  and  JPrantl  are  placed  in 
one  order,  Auriculariineae. 


FUNGI  CONTINUED:    CLASSIFICATION.  2 19 

^ 

4.  SUBCLASS  EUBASIDIOMYCETES. 

460.  Order  Dacryomycetales  (Dacryomycetineae). — This  order  includes 
certain  fungi  of  a  gelatinous  or  waxy  consistency,  usually  of  bright  colors. 
They  resemble  the  Tremellales,  but  the  basidia  are  slender  and  fork  into 
two  long  sterigmata.     (Example,   Dacryomyces.)     Gyrocephalus  rufus  is 
quite  a  large  plant,  10-15  cm-  high)  growing  on  the  ground  in  woods. 

461.  Order  Exobasidiales  (Exobasidiinese). — The  fungus  causing  azalea 
apples  is  an  example  (Exobasidium). 

462.  Order  Hymenifijes  (Hymenomycetinese). — In  this  order  the  basidia 
are  usually  club-shaped  and  undivided,  and  bear  usually  four  spores  on 
the  end  (sometimes  two  or  six).     There  are  several  families. 

463.  Family  Thelephoraceae. — The  fruit  bodies  are  more  or  less  mem- 
branous and  spread  over  wood  or  the  ground,  or  somewhat  leaflike,  grow- 
ing on  wood  or  the  ground.     The  fruiting  surface  is  nearly  or  quite  even, 
and  occupies  the  under  side  of  the  leaflike  bodies  (Stereum,  Thelephora) 
or  the  outside  of  the  forms  spread  out  on  wood  (Corticium,'Coniophora). 

464.  Family  Clavariaceae. — This  order  includes  the  fairy  clubs,  and  some 
of  the  coral  fungi.     The  larger  number  of  species  are  in  one  genus  (Clava- 
ria,  fig.  248). 

465.  Family  Hydnaceae. — The  fungi  of  this  order  are  known  as  "hedge- 
hog" fungi,  because  of  the  numerous  awl-like  teeth  or  spines  over  which 
the  fruiting  surface  is  spread,  as  in  Hydnum  (figs.  246,  247). 

466.  Family  Polyporacese. — The  tube-bearing  fungi   (Polyporus,   Bole- 
tus, etc.,  fig.  245). 

467.  Family  Agaricaceae. — The  gill-bearing  fungi  (Agaricus,  Amanita, 
etc.,  see  Chapter  XXI). 

The  above  five  orders,  according  to  the  earlier  classification  (still  used  at 
the  present  time  by  some),  made  up  the  order  Hymenomycetes,  while  the 
following  five  orders  made  up  the  Gasteromycetes.  The  Hymenomycetes, 
according  to  this  system,  included  those  plants  in  which  the  fruiting  portion 
(hymenium)  is  either  exposed  from  the  first,  or  if  covered  by  a  veil  or  volva 
(as  in  Agaricus,  Amanita,  etc.)  this  ruptures  and  exposes  the  fruiting  sur- 
face before,  or  at  the  time  of,  the  ripening  of  the  spores,  while  the  Gaster- 
omycetes included  those  in  which  the  fruit  body  is  closed  until  after  the 
maturity  of  the  spores. 

468.  Order  Phallales  (Phallinese). — The    "stink-horn"  fungi,  or  "buz- 
zard's nose."     Usually  foul-smelling  fungi,  the  fruiting  portion  borne  aloft 
on  a  stout  stalk,  and  dissolving  (Dictyophora,  Ithyphallus,  etc.). 

469.  Order  Hymenogastrales  (Hymenogastrineee). — The  basidia  form  a 
distinct  hymenium  on  walls  of  chambers,  which  do  or  do  not  break  down 
at  maturity,  but  there  are  no  sterile  threads  forming  a  capillitium.     Some 
of  the  plants  resemble  Boletus  or  Agaricus  in  the  way  the  fruit  bodies  open 
(Secotium,  etc.),  while  others  open  irregularly  on  the  surface  (Rhizopogon)  or 


2 2O  MO RPHOLOG  Y. 

like  an  earth  star  (Sclerogaster),  or  portions  of  the  surface  become  gelatin- 
ized (Phallogaster).  The  last-named  one  grows  on  very  rotten  wood,  while 
most  of  the  others  grow  on  the  ground. 

470.  Order   Lycoperdales    (Lycoperdineae). — These    include    the  "puff- 
balls,"  or  "devil's  snuff-box"  (Lycoperdon),  and  the  earth  stars  (Geaster). 
The  basidia  form  a  distinct  hymenium,  but  at  maturity  the  entire  inner  por- 
tion of  the  plant  (except  certain  peculiar  threads,  the  capillitium)  disinte- 
grates and  with  the  spores  forms  a  powdery  mass. 

471.  Order  Nidulariales  (Nidulariineee). — These  are  known  as  bird-nest 
fungi.     The  fruit  body  when  mature  is  cup-shaped,  or  goblet-shaped,  and 
contains  minute  flattened  circular  bodies  (peridiola)  containing  the  spores. 
The  intermediate  portions  of  the  fruit  body  disintegrate  and  set  the  peri- 
diola free,  which  then  lie  in  the  cup-shaped  base  like  eggs  in  a  nest. 

472.  Order    Plectobasidiales    (Plectobasidiineae). — The    basidia   do    not 
form  a  definite  hymenium,  but  are  interwoven  with  the  threads  inside,  or 
are  collected  into  knot-like  groups.     (Examples:   Calostoma,   Tulostoma, 
Astraeus,  Sphaerobolus,  etc.) 

472a.  Lichens. — The  plant  body  of  the  lichens  (see  paragraphs  200. 
201)  consists  of  two  component  parts,  the  one  a  fungus,  the  other  an  alga. 
The  fructification  is  that  of  the  fungus.  The  fruit  body  shows  the  lichens 
to  be  related  some  to  the  Ascomycetes,  others  to  the  Hymenomycetes,  and 
Gasteromycetes.  They  are  usually  classified  as  a  distinct  class  or  order 
from  the  fungi,  but  a  natural  arrangement  would  distribute  them  in  sev- 
eral of  the  orders  above.  .Their  special  relationship  with  these  orders  has 
not  been  satisfactorily  worked  out.  For  the  present  they  are  arranged  as 
follows: 
Ascolichenes. 

Pyrenocarpous  lichens  (those  with  a  fruit  body  like  the  Pyrenomycetes). 

Gymnocarpous  lichens  (those  with  a  fruit  body  like  the  Discomycetes). 
Hymenolichenes  (those  with  a  fruit  bod}  like  the  Hymenomycetes). 
Gasterolichenes  (those  with  a  fruit  body  like  the  Gasteromycetes). 

From  a  vegetative  standpoint  there  are  two  types  according  to  the  dis- 
tribution of  the  elements. 

i st.  Where  the  fungal  and  algal  elements  are  evenly  distributed  in  the 
plant  body  the  lichen  is  said  to  be  homoiomerous.  There  are  two  types  of 
these: 

a.  Filamentous  lichens,  example,  Ephebe  pubescens. 

b.  Gelatinous  lichens,  example,  Collema  (with  the  alga  nostoc),  Physma 
(with  the  Chroococcaceae). 

2d.  Where  the  elements  are  stratified,  as  in  Parmelia,  etc.,  the  lichen  is 
said  to  be  heteromerous.  In  these  there  are  three  types: 

a.  Crustaceous  lichens,  the  plant  body  is  in  the  form  of  a  thin  incrusta 
tion  on  rocks,  etc. 


FUNGI  CONTINUED:    CLASSIFICATION. 


22i 


b.  Foliaceous  lichens,  the  plant  body  is  leaflike  and  lobed  and  more  or  less 
loosely  attached  by  rhizoids:   Parmelia,  Peltigera-- etc. 


Fig.  2510. 
Rock  lichen  (Parmelia  contigua). 

c.  Fruticose  lichens,   tte  plant  body  is  filamentous  or  band-like  and 
branched,  as  in  Usnea,  Cladcnia,  etc. 


CHAPTER  XXIII. 
j*     .LIVERWORTS    (HEPATICyE). 

•>v  ""'  '    •  """•     •       .       lV> 

473.  We  come  now  to  the  study  of  representatives  of  another 
group  of  plants,  a  few  of  which  we  examined  in  studying  the  organs 
of  assimilation  and  nutrition.      I  refer  to  what  are  called  the  liver- 
worts.     Two  of  these  liverworts  belonging  to  the  genus  riccia 
are  illustrated  in  figs.  30,  252. 

]) 

Riccia. 

474.  Form  of  the  floating  riccia  (R.  fluitans). — The  gen- 
eral form  of  floating  riccia  is  that  of  a  narrow,  irregular,  flattened, 
ribbon-like  object,  which   forks  repeatedly,   in  a  dichotomous 
manner,  so  that  there  are  several  lobes  to  a  single  plant.      It 
receives  its  name  from  the  fact  that  at  certain  seasons  of  the  year 
it  may  be  found  floating  on  the  water  of  pools  or  lakes.      When 
the  water  lowers  it  comes  to  rest  on  the  damp  soil,  and  rhizoids 
are  developed  from  the  under  side.     Now  the  sexual  organs,  and 
later  the  fruit  capsule,,  are  developed. 

475.  Form  of  the  circular    riccia    (R.  crystallina). — The 
circular  riccia  is  shown  in  fig.  252.     The  form  of  this  one  is  quite 
different  from  the  floating  one,  but  the  manner  of  growth  is  much 
the  same.     The  branching  is  more  compact  and  even,  so  that  a  cir- 
cular plant   is  the  result.     This  riccia  inhabits  muddy  banks, 
lying  flat  on  the  wet  surface,  and  deriving  its  soluble  food  by 
means  of  the  little  rootlets  (rhizoids)  which  grow  out  from  the 
under  surface. 

Here  and  there  on  the  margin  are  narrow  slits,  which  extend 


LIVERWORTS:   RICCIA. 


223 


Fig.  252. 
Thallus  of  Riccia  crystallina. 


nearly  to  the  central  point.  They  are  not  real  slits,  however,  foi 
they  were  formed  there  as  the  plant  grew.  Each  one  of  these 
V-shaped  portions  of  the  thal- 
lus  is  a  lobe,  and  they  were 
formed  in  the  young  condition 
of  the  plant  by  a  branching 
in  a  forked  manner.  Since 
growth  took  place  in  all  direc- 
tions radially  the  plant  be- 
came circular  in  form.  These 
large  lobes  we  can  see  are 
forked  once  or  twice  again, 
as  shown  by  the  seeming 
shorter  slits  in  the  margin. 

476.  Sexual  organs.  —  In 
order  to  study  the  sexual  organs  we  must  make  thin  sections 
through  one  of  these  lobes  lengthwise  and  perpendicular  to  the 
thallus  surface.  These  sections  are  mounted  for  examination 
with  the  microscope. 

477.  Archegonia. — We  are  apt  to  find  the  organs  in  various  stages  of  de- 
velopment, but  we  will  select  one  of  the  flask-shaped  structures  shown  in  fig. 
253  for  study.     This  flask-shaped  body  we  see  is  entirely  sunk  in  the  tissue 
of  the  thallus.     This  structure  is  the  female  organ,  and  is  what  we  term  in 
these  plants  the  archegonium.     It  is  more  complicated  in  structure  than  the 
oogonium.     The  lower  portion  is  enlarged  and  bellied  out,  and  is  the  venter 
of  the  archegonium,  while  the  narrow  portion  is  the  neck.     We  here  see  it  in 
section.     The  wall  is  one  cell  layer  in  thickness.     In  the  neck  is  a  canal, 
and  in  the  base  of  the  venter  we  see  a  large  rounded  cell  with  a  distinct 
and  large  nucleus.     This  cell  is  the  egg  cell. 

478.  Antheridia. — The  antheridia  are  also  borne  in  cavities  sunk  in  the 
tissue  of  the  thallus.     There  is  here  no  illustration  of  the  antheridium  of  this 
riccia,  but  fig.  259  represents  an  antheridium  of  another  liverwort,  and  there 
is  not  a  great  difference  between  the  two  kinds.    Each  one  of  those  little  rect- 
angular sperm  mother  cells  in  the  antheridium  changes  into  a  swiftly  moving 
body  like  a  little  club  with  two  long  lashes  attached  to  the  smaller  end    By 
the  violent  lashing  of  these  organs  the  spermatozoid  is  moved  through  the  water, 
or  moisture  which  is  on  the  surface  of  the  thallus.    It  moves  through  the  canal 
of  the  archegonium  neck  and  into  the  egg,  where  it  fuses  with  the  nucleus  of 
the  egg,  and  thus  fertilization  is  effected. 


224 


MORPHOLOG  Y. 


479.  Embryo. — In  the  plants  which  we  have  selected  thus  far  for  study, 
the  egg,  immediately  after  fecundation,  we  recollect,  passed  into  a  resting 
state,  and  was  enclosed  by  a  thick  protecting  wall.  But  in  riccia,  and  in  the 
other  plants  of  the  group  which  we  are  now  studying,  this  is  not  the  case. 


Fig.  253. 

Archegonium  of  riccia,  showing  neck, 
venter,  and  the  egg;  archegonium  is  partly 
surrounded  by  the  tissue  of  the  thallus. 
(Riccia  crystallina.) 


Fig.  254. 

Young  embryo  (sporogoni- 
um)  of  riccia,  within  the  venter 
of  the  archegonium  ;  the  latter 
has  now  two  layers  of  cells. 
(Riccia  crystallina.) 


The  egg,  on  the  other  hand,  after  acquiring  a  thin  wall,  swells  up  and  fills 
the  cavity  of  the  venter.  Then  it  divides  by  a  cross  wall  into  two  cells. 
These  two  grow,  and  divide  again,  and  so  on  until  there  is  formed  a  quite 
large  mass  of  cells  rounded  in  form  and  still  contained  in  the  venter  of  the 
archegonium,  which  itself  increases  in  size  by  the  growth  of  the  cells  of  the 
wall. 

480.  Sporogonium  of  riccia. — The  fruit  of  riccia,  which  is 
developed  from  the  fertilized  egg  in  the  archegonium,  forms  a 
rounded  capsule  still  enclosed  in  the  venter  of  the  archegonium, 
which  grows  also  to  provide  space  for  it.  Therefore  a  section 
through  the  plant  at  this  time,  as  described  for  the  study 
of  the  archegonium,  should  show  this  capsule.  The  capsule 
then  is  a  rounded  mass  of  cells  developed  from  the  egg.  A  sin- 
gle outer  layer  of  cells  forms  the  wall,  and  therefore  is  sterile. 


LIVERWORTS:   RICCIA. 


225 


All  the  inner  cells,  which  are  richer  in  protoplasm,  divide  into 
four  cells  each.  Each  of  these  cells  becomes  a  spore  with  a  thick 
wall,  and  is  shaped  like  a  triangular  pyramid  whose  sides  are  of 
the  same  extent  as  the  base  (tetrahedral).  These  cells  formed  in 


Fig.  255- 

Nearly  mature  sporogonium  of  Riccia  crystallina ; 
mature  spore  at  the  right. 


Fig.  256. 

Riccia  glauca ;  archegonium 
containing  nearly  mature  spo- 
rogonium. sg;  spore-producing 
cells  surrounded  by  single  layer 
of  sterile  cells,  the  wall  of  the 
sporogonium . 


fours  are  the  scores.  At  this  time  the  wall  of  the  spore-case  dis- 
solves, the  spores  separate  from  each  other  and  fill  the  now  en- 
larged venter  of  the  archegonium.  When  the  thallus  dies  they 
are  liberated,  or  escape  between  the  loosely  arranged  cells  of 
the  upper  surface. 

481.  A  new  phase  in  plant  life. — Thus  we  have  here  in  the 
sporogonium  of  riccia  a  very  interesting  phase  of  plant  life,  in 
which  the  egg,  after  fertilization,  instead  of  developing  directly 
into  the  same  phase  of  the  plant  on  which  it  was  formed, 
grows  into  a  quite  new  phase,  the  sole  function  of  which  is  the 
development  of  spores.  Since  the  form  of  the  plant  on  which  the 
sexual  organs  are  developed  is  called  the  gametopkytet  this  new 
phase  in  which  the  spores  are  developed  is  termed  the  sporo- 
phyte. 

Now  the  spores,  when  they  germinate,  develop  the  gameto- 
phyte,  or  thallus,  again.  So  we  have  this  very  interesting  condi- 


226  MORPHOLOG  Y. 

tion  of  things,  the  thallus  (gametophyte)  bears  the  sexual  organs 
and  the  unfertilized  egg.  The  fertilized  egg,  starting  as  it  does 
from  a  single-celled  stage,  develops  the  sporogonium  (sporo- 
phyte).  Here  the  single-cell  stage  is  again  reached  in  the  spore, 
which  now  develops  the  thallus. 

482.  Riccia  compared  with  coleochaete,  cedogonium,  etc. — We  have  said 
that  in  the  sporogonium  of  riccia  we  have  formed  a  new  phase  in  plant  life. 
If  we  recur  to  our  study  of  coleochaete  we  may  see  that  there  is  here  possibly 
a  state  of  things  which  presages,  as  we  say,  this  new  phase  which  is  so  well 
formed  in  riccia.  We  recollect  that  after  the  fertilized  egg  passed  the  period 
of  rest  it  formed  a  small  rounded  mass  .of  cells,  each  of  which  now  forms  a 
zoospore.  The  zoospore  in  turn  develops  the  normal  thallus  (gametophyte) 
of  the  coleochaete  again.  In  coleochaete  then  we  have  two  phases  of  the 
plant,  each  having  its  origin  in  a  one-celled  stage.  Then  if  we  go  back 
to  oedogonium,  we  remember  that  the  fertilized  egg,  before  it  developed 
into  the  oedogonium  plant  again  (which  is  the  gametophyte),  at  first  divides 
into  four  cells  which  become  zoospores.  These  then  develop  the  cedogonium 
plant. 

Note.  Too  much  importance  should  not  be  attached  to  this  seeming  ho. 
mology  of  the  sporophyte  of  cedogonium,  coleochaete,  and  riccia,  for  the  nu. 
clear  phenomena  in  the  formation  of  the  zoospores  of  oedogonium  and  coleo. 
chaete  are  not  known.  They  form,  however,  a  very  suggestive  series. 


Marchantia. 

483.  The  marchantia  (M.  polymorpha)  has  been  chosen  for 
study  because  it  is  such  a  common  and  easily  obtained  plant,  and 
also  for  the  reason  that  with  comparative  ease  all  stages  of 
development  can  be  obtained.  It  illustrates  also  very  well  cer- 
tain features  of  the  structure  of  the  liverworts. 

The  plants  are  of  two  kinds,  male  and  female.  The  two  dif- 
ferent organs,  then,  are  developed  on  different  plants.  In 
appearance,  however,  before  the  beginning  of  the  structures 
which  bear  the  sexual  organs  they  are  practically  the  same.  The 
thallus  is  flattened  like  nearly  all  of  the  thalloid  forms,  and 
branches  in  a  forked  manner.  The  color  is  dark  green,  and 
through  the  middle  line  of  the  thallus  the  texture  is  different 
from  that  of  the  margins,  so  that  it  possesses  what  we  term  a 


LIVER  IVOR  1  'S  :   MA X CHA  N  TIA . 


227 


midrib,  as  shown  in  figs.  257,  261.  The  growing  point  of  the 
thallus  is  situated  in  the  little  depression  at  the  free  end.  If  we 
examine  the  upper  surface  with  a  hand 
lens  we  see  diamond-shaped  areas,  and 
at  the  center  of  each  of  these  areas  are 
the  openings  known  as  the  stomates. 

484.  Antheridial  plants. — One  of 
the  male  plants  is  figured  at  257.      It 
bears   curious  structures, 
each  held  aloft  by  a  short 
stalk.     These  are  the  an- 
theridial    recep- 
tacles (or   male 
gametophores). 
Each  one  is  cir- 
cular, thick,  and 
shaped       some-  Fig.  257. 

what    like    a,    bl*  Male  plant  of  marchantia  bearing  anthericLophores. 

convex  lens.  The  upper  surface  is  marked  by  radiating  fur- 
rows, and  the  margin  is  crenate.  Then  we  note,  on  careful 
examination  of  the  upper  surface,  that  there  are  numerous  minute 
openings.  If  we  make  a  thin  section  of  this  structure  perpen- 


Fig.  258. 

Section  of  antheridial  receptacle  from  male  plant  of  Marchantia  polymorpha,  showing 
cavities  where  the  antheridia  are  borne. 

dicular  to  its  surface  we  shall  be  able  to  unravel  the  mystery  of 
its  interior.  Here  we  see,  as  shown  in  fig.  258,  that  each  one 
of  these  little  openings  on  the  surface  is  an  entrance  to  quite 


228 


MO  RP HO  LOG  Y. 


a  large  cavity.  Within  each  cavity  there  is  an  oval  or  ellip- 
tical body,  supported  from  the  base  of  the  cavity  on  a  short 
stalk.  This  is  an  antheridium,  and  one  of  them  is  shown  still 
more  enlarged  in  fig.  259.  This  shows  the  structure  of  the 
antheridium,  and  that  there  are  within  several  angular  areas, 
which  are  divided  by  numerous  straight  cross-lines  into  countless 
tiny  cuboidal  cells,  the  sperm  mother  cells.  Each  of  these,  as 
stated  in  the  former  chapter,  changes  into  a  swiftly  moving  body 
resembling  a  serpent  with  two  long  lashes  attached  to  its  tail. 

485.  The  way  in  which  one  of  these  sperm  mother  cells  changes  into  this 
spermatozoid  is  very  curious.    We  first  note  that  a  coiled  spiral  body  is  appear- 


Fig.  259. 

Section  of  antheridium  of  mar- 
chantia, showing  the  groups  of 
sperm  mother  cells. 


Fig.  260.  . 

Spermatozoids  of  marchantia, 
uncoiling  and  one  extended,  show- 
ing the  two  cilia. 


ing  within  the  thin  wall  of  the  cell,  one  end  of  the  coil  larger  than  the  other. 
The  other  end  terminates  in  a  slender  hair-like  outgrowth  with  a  delicate  vesi- 
cle attached  to  its  free  end.  This  vesicle  becomes  more  and  more  extended 
until  it  finally  breaks  and  forms  two  long  lashes  which  are  clubbed  at  their 
free  ends  as  shown  in  fig.  260.  9 

486.  Archegonial  plants. — In  fig.  261  we  see  one  of  the 
female  plants  of  marchantia.  Upon  this  there  are  also  very 
curious  structures,  which  remind  one  of  miniature  umbrellas. 
The  general  plan  of  the  archegonial  receptacle  (or  female 


LIVERWORTS:    MARCHANTIA.  22$ 

gametophore),  for  this  is  what  these  structures  are,  is  similar  to 
that  of  the  antheridial  receptacle,  but  the  rays  are  more  pro- 
nounced, and  the  details  of  structure  are  quite  different,  as  we 
shall  see.  Underneath  the  arms  there  hang  down  delicate 
fringed  curtains.  If  we  make  sections  of  this  in  the  same  direc- 


Fig.  261. 
Marchantia  polymorpha,  female  plants  bearing  archegoniophores. 

tion  as  we  did  of  the  antheridial  receptacle,  we  shall  be  able  to 
find  what  is  secreted  behind  these  curtains.  Such  a  section  is 
figured  at  266.  Here  we  find  the  archegonia,  but  instead  of 
being  sunk  in  cavities  their  bases  are  attached  to  the  under 


230 


MOKPHOLOG  Y. 


surface,  while  the  delicate,  pendulous  fringes  afford  them  pro- 
tection from  drying.  An  archegonium  we  see  is  not  essentially 
different  in  marchantia  from  what  it  is  in  riccia,  and  it  will  be 
interesting  to  learn  whether  the  sporogonium  is  essentially  dif- 
ferent from  what  we  find  in  riccia. 

487.  Homology  of  the  gametophore  of  marchantia. — To  seethe  relation 

of  the  gametophore  to  the  thallus  of 
marchantia  take  portions  of  the 
thallus  bearing  the  female  recepta,- 
cle.  On  the  under  side  note  that 
the  prominent  midrib  continues  be- 
yond the  thin  lateral  expansions  and 
arches  upward  in  the  sinus  or  notch 
at  the  end,  or  at  the  side  where  the 
branch  of  the  thallus  has  continued 
to  grow  beyond.  The  stalk  of  the 
gametophore  is  then  a  continuation 
of  the  midrib  of  the  thallus.  On 
the  apex  of  this  are  organized  sev- 
eral radial  growing  points  which 
develop  the  digitate  or  ray-like 
receptacle.  The  gametophore  is 
thus  a  specialized  branch  of  the 
thallus.  When  young,  or  in  many 
cases  when  nearly  or  quite  mature, 
the  gametophore,  as  one  looks  at 
the  upper  surface  of  the  thallus, 
appears  to  arise  from  the  upper 
surface,  as  in  fig.  261.  This  is 
because  the  thin  lateral  expansions 
Marchantia  polymorpha,  showing  origin  of  the  thallus  project  forward  and 
cf  gametophore.  overlap  in  advance  of  the  stalk.  It 

is  sometimes  necessary  to  tear  these  overlapping  edges  apart  to  see  the 
real  origin  of  the  gametophore.  But  in  quite  old  plants  these  expanded 
portions  are  farther  apart  and  show  clearly  that  the  stalk  arises  from  the 
midrib  below  and  arches  upward  in  the  sinus,  as  in  fig.  262. 


CHAPTER  XXIV. 

LIVERWORTS  CONTINUED. 

488*  Sporogonium  of  marchantia. — If  we  examine  the  plant 
shown  in  fig.  181  we  shall  see  oval  bodies  which  stand  out  be- 


Fig.  263. 

Archegonial  receptacles  of  marchantia  bearing  ripe  sporogonia.  The 
capsule  of  the  sporogonium  projects  outside,  while  the  stalk  is  attached  to 
the  receptacle  underneath  the  curtain.  In  the  left  figure  two  of  the 
capsules  have  burst  and  the  elaters  and  spores  are  escaping. 

tween  the  rays  of  the  female  receptacle,  supported 
stalks.  These  are  the  sporogonia,  or 
spore-cases.  We  judge  at  once  that  they  are  quite 
different  from  those  which  we  have  studied  in 
riccia,  since  those  were  not  stalked.  We  can  see 
that  some  of  the  spore-cases  have  opened,  the  wall 
splitting  down  from  the  apex  in  several  lines.  This 
is  caused  by  the  drying  of  the  wall.  These  tooth- 
like  divisions  of  the  wall  now  curl  backward,  and 
can  see  the  yellowish  mass  of  the  spores  in  slow  motion, 

231 


232 


MORPHOLOG  V. 


falling  here  and  there.  It  appears  also  as  if  there  were  twisting 
threads  which  aided  the  spores  in  becoming  freed  from  the 
capsule. 


Fig.  264. 

Section  of  archegpnial  receptacle  of  Marchantia  polymorpha;  ripe 
sporogonia.  One  is  open,  scattering  spores  and  elaters;  two  are 
still  enclosed  in  the  wall  of  the  archegonium.  The  junction  of  v*ie 
stalk  of  the  sporogonium  with  the  receptacle  is  the  point  of  attach- 
ment of  the  sporophyte  of  marchantia  with  the  gametophyte. 

489.  Spores  and  elaters. — If  we  take  a  bit 
of  this  mass  of  spores  and  mount  it  in  water 
for  examination  with  the  microscope,  we  shall 
see  that,   besides  the  spores,  there  are  very 
peculiar     thread-like    bodies, 

the  markings  of  which  remind 
one  of  a  twisted  rope.    These 
are  very  long  cells   from  the 
inner  part  of  the  spore-case, 
and    their    walls 
are  marked  by  spi- 
ral    thickenings. 
This  causes  them 
indrying,andalso 
when  they  absorb 

3  .  Fig.  265. 

moisture,   tO  tWISt       Elater  and  spore  of  marchantia.    sp,  spore ;  me,  mother-cell  of 

and   curl    in    all spores>  showing  partly  formed  spores' 

sorts  of  ways.     They  thus  aid  in  pushing  the  spores  out  of  the 

capsule  as  it  is  drying. 

490.  Sporophyte  of  marchantia  compared  with  riecia.— 
We  must  recollect  that  the  sporogonium  in  marchantia  is  larger 
than  in  riccia,  and  that  it  is  also  not  lying  in  the  tissue  of  the 
thallus,  but  is  only  attached  to  it  at  one  side  by  a  slender  stalk. 


LIVERWORTS:   MARCHANTIA. 


233 


This  shows  us  an  increase  in  the  size  and  complex  structure  of 
this  new  phase  of  the  plant,  the  sporophyte.  This  is  one  of  the 
very  interesting  things  which  we  have  to  note  as  we  go  on  in  the 
study  of  the  higher  plants. 


Fig.  266. 

Ma.  chantia  polymorpha,  archegonium  at  the  left  with  egg ;  archegonium  at  the  right  with 
young  sporogonium ;  /,  curtain  which  hangs  down  around  the  archegonia ;  et  egg;  v,  venter 
of  archegonium ;  »,  neck  of  archegonium ;  sp,  young  sporogonium. 

491.  Sporophyte  dependent  on  the  gametophyte  for  its  nutri- 
ment.— We  thus  see  that  at  no  time  during  the  development  of  the 
sporogonium  is  it  independent  from  the  gametophyte.     This  new 
phase  of  plants  then,  the  sporophyte,  has  not  yet  become  an  in- 
dependent plant,  but  must  rely  on  the  earlier  phase  for  sustenance. 

492.  Development  of  the  sporogonium. — It  will   be  interesting  to  note 
briefly  how  the  development  of  the  marchantia  sporogonium  differs  from  that 
of  riccia.  The  first  division  of  the  fertilized  egg  is  the  same  as  in  riccia,  that 
is  a  wall  which  runs  crosswise  of  the  axis  of  the  archegonium  divides  it 
into  two  cells.     In  marchantia  the  cell  at  the  base  develops  the  stalk,  so 
that  here  there   is  a  radical  difference.     The  outer  cell  forms  the  capsule. 
But  here  after  the  wall  is  formed  the  inner  tissue  does  not  all  go  to  make 
spores,  as  is  the  case  with  riccia.     But  some  of  it  forms  the  elaters.     While 
in  riccia  only  the  outside  layer  of  cells  of  the  sporogonium  remained  sterile, 
in  marchantia  the  basal  half  of  the  egg   remains  completely  sterile  and 


234 


MORPHOLOG  Y. 


develops  the  stalk,  ana  in  the  outer  half  the  part  which  is  formed  from  some 
of  the  inner  tissue  is  also  sterile. 


Fig.  267. 

Section  of  developing  sporogonia  of  marchantia ;  nt,  nutritive  tissue  of  gametophyte  ;  st, 
sterile  tissue  of  sporophyte  ;  sp,  fertile  part  of  sporophyte  ;  va,  enlarged  venter  of  arche- 
gonium. 

493.  Embryo. — In  the  development  of  the  embryo  we  can  see  all  the  way 
through  this  division  line  between  the  basal  half,  which  is  completely  sterile, 
and  the  outer  half,  which  is  the  fertile  part.  In  fig.  267  we  see  a  young 
embryo,  and  it  is  nearly  circular  in  section  although  it  is  composed  of 
numerous  cells.  The  basal  half  is  attached  to  the  base  of  the  inner  surface 
of  the  archegonium,  and  at  this  time  the  archegonium  still  surrounds  it.  The 
archegonium  continues  to  grow  then  as  the  embryo  grows,  and  we  can  see 
the  remains  of  the  shrivelled  neck.  The  portion  of  the  embryo  attached  to 
the  base  of  the  archegonium  is  the  sterile  part  and  is  called  the  "  foot,"  and 
later  develops  the  stalk.  The  sporogonium  during  all  the  stages  of  its 
development  derives  its  nourishment  from  the  gametophyte  at  this  point  of 


LIVERWORTS:   MARCHANTIA.  235 

attachment  at  the  base  of  the  archegonium.  Soon,  as  shown  in  fig.  267  at 
the  right,  the  outer  portion  of  the  sporogonium  begins  to  differentiate  into 
the  cells  which  form  the  elaters  and  those  which  form  spores.  These  lie  in 
radiating  lines  side  by  side,  and  form  what  is  termed  the  archesporium.  Each 
fertile  cell  forms  four  spores  just  as  in  riccia.  They  are  thus  called  the 
mother  cells  of  the  spores,  or  spore  mother  cells. 

494.  How  marchantia  multiplies. — New  plants  of  marchantia  are  formed 
by  the  germination  of  the  spores,  and  growth  of  the  same  to  the  thallus. 
The  plants  may  also  be  multiplied  by  parts  of  the  old  ones  breaking  away 
by  the  action  of  strong  currents  of  water,  and  when  they  lodge  in  suitable 
places  grow  into  well-formed  plants.     As  the  thallus  lives  from  year  to  year 
and  continues  to  grow  and  branch  the  older  portions  die  off,  and  thus  sepa- 
rate plants  may  be  formed  from  a  former  single  one. 

495.  Buds,  or  gemmae,  of  marchantia. — But  there  is  another  way  in  which 
marchantia  multiplies  itself.     If  we  examine  the  upper  surface  of  such  a 


Fig.  268. 
Marchantia  plant  with  cupules  and  gemmae  ;  rhizoids  below. 

plant  as  that  shown  in  fig.  268.  we  shall  see  that  there  are  minute  cup- 
shaped  or  saucer-shaped  vessels,  and  within  them  minute  green  bodies. 
If  we  examine  a  few  of  these  minute  bodies  with  the  microscope  we  see  that 
they  are  flattened,  biconvex,  and  at  two  opposite  points  on  the  margin  there 
is  an  indentation  similar  to  that  which  appears  at  the  growing  end  of 
the  old  marchantia  thallus.  These  are  the  growing  points  of  these  little 
buds.  When  they  free  themselves  from  the  cups  they  come  to  lie  on  one 


236 


MORPHOLOG  Y. 


side.  It  does  not  matter  on  what  side  they  lie,  for  whichever  side  it  is,  that 
will  develop  into  the  lower  side  of  the  thallus,  and  forms  rhizoids,  while  the 
upper  surface  will  develop  the  stomates. 


Leafy-stemmed  liverworts. 

496.  We  should  now  examine  more  carefully  than  we  have 
done  formerly  a  few  of  the    leafy-stemmed   liverworts   (called 
foliose  liverworts). 

497.  Frullania  (Fig.  32). — This  plant  grows  on  the  bark  of 
logs,  as  well  as  on  the  bark  of  standing  trees.      It  lives  in  quite 

dry  situations. 
If  we  examine 
the  leaves  we 
will  see  how  it  is 
able  to  do  this. 
We  note  that 
there  are  two 
rows  of  lateral 
leaves,  which 
are  very  close 
together,  so 
close  in  fact  that 
they  overlap 
like  the  shingles 
on  a  roof. 
Then,  as  the 


Fig.  269. 


Section  of  thallus  of  marchantia.     A,  through  the  middle  portion  , 
B,  through  the  marginal  portion  ;  /,  colorless  layer ;  chl,  chlorophyll  creeping     Stems 
layer;   sp,  stomate ;   /t,  rhizoids;    b,  leaf-like   outgrowths  on  under 

side  (Goebel).  he  very  close  to 

the  bark  of  the  tree,  these  overlapping  leaves,  which  also 
hug  close  to  the  stem  and  bark,  serve  to  retain  moisture 
which  trickles  down  the  bark  during  rains.  If  we  examine 
these  leaves  from  the  under  side  as  shown  in  fig.  34,  we  see 
that  the  lower  or  basal  part  of  each  one  is  produced  into  a 
peculiar  lobe  which  is  more  or  less  cup-shaped.  This  catches 
water  and  holds  it  during  dry  weather,  and  it  also  holds  moisture 
which  the  plant  absorbs  during  the  night  and  in  damp  days. 


FOLIO SE   LIVERWORTS. 


237 


There  is  so  much  moisture  in  these  little  pockets  of  the  under 
side  of  the  leaf  that  minute  animals  have  found  them  good  places 
to  live  in,  and  one  frequently  discovers  them  in  this  retreat. 
There  is  here  also  a  third  row  of  poorly  developed  leaves  on  the 
under  side  of  the  stem. 

498.  Porella. Growing   in   similar   situations  is   the   plant    known    as 

porella.    Sometimes  there  are  a  few  plants 
in  a  group,  and  at  other  times  large  mats 
occur  on  the  bark  of  a  trunk.     This  plant, 
porella,  also  has  closely  overlapping  leaves 
in  rows  on  opposite  sides  of  the  stem,  and 
the  lower  margin  of  each  leaf  is  curved 
under  somewhat   as 
in  frullania,  though 
the  pocket  is  not  so 
well  formed. 

The  larger  plants 
are  female,  that  is 
they  bear  archego- 
nia,  while  the  male 
plants,  those  which 
bear  antheridia,  are 
smaller  and  the  an- 
theridia are  borne 
on  small  lateral 
branches.  The  an- 
theridia are  borne 
in  the  axils  of  the 
leaves.  Others  of 
the  leafy-stemmed 
liverworts  live  in 
damp  situations. 
Some  of  these,  as 
Cephalozia,  grow  on  damp  rotten  logs.  Cephalozia  is  much  more  delicate, 
and  the  leaves  are  farther  apart.  It  could  not  live  in  such  dry  situations 
where  the  frullania  is  sometimes  found.  If  possible  the  two  plants  should  be 
compared  in  order  to  see  the  adaptation  in  the  structure  and  form  to  their 
environment. 

499.  Sporogonium  of  a  foliose  liverwort. — The  sporogonium 
of  the  leafy-stemmed  liverworts  is  well  represented  by  that  of 
several  genera.  We  may  take  for  this  study  the  one  illustrated 


I'ig.  270. 

Thallus  of  a  thalloid  liverwort  (blasia)  showing  lobed 
margin  of  the  frond,  intermediate  between  thalloid  and 
foliose  plant. 


MORPHOLOG  Y. 


in  fig.  274,  but  another  will  serve  the  purpose  just  as  well.  We 
note  here  that  it  consists  of  a  rounded  capsule  borne  aloft  on  a 
long  stalk,  the  stalk  being  much  longer  proportionately  than  in 
marchantia.  At  maturity  the  capsule  splits  down  into  four 


Fig.  272. 

Antheridium  of  a  foliose  liverwort  (jun 
germannia). 


Fig.  271. 

Foliose  liverwort,  male  plant  showing  anthe- 
ridia  in  axils  of  the  leaves  (a  jungermannia). 


Fig.  273. 

Foliose  liverwort,  female  plant  with 
rhizoids. 


quadrants,  the  wall  forming  four  valves,  which  spread  apart  from 
the  unequal  drying  of  the  cells,  so  that  the  spores  are  set  free,  as 
shown  in  fig.  276.  Some  of  the  cells  inside  of  the  capsule  de- 
velop elaters  here  also  as  well  as  spores.  These  are  illustrated 
in  fig.  278. 

500.  In  this  plant  we  see  that  the  sporophyte  remains  attached 


FOLIO SE  LIVERWORTS. 


239 


to  the  gametophyte,  and  thus  is  dependent  on  it  for  sustenance. 
This  is  true  of  all  the  plants  of  this 
group.  The  sporophyte  never  becomes 
capable  of  an  independent  existence, 
and  yet  we  see  that  it  is  becoming 
larger  and  more  highly  differentiated 
than  in  the  simple  riccia. 


Fig.  275. 

Opening  capsule 
showing  escape  of 
spores  and  elaters. 


Fig.  276. 

Capsule  parted  down 
to  the  stalk. 


Fig.  274. 

Fruiting  plant  of  a  foliose  liver-  pjg  ^TJ.                                   Fig.  278. 
wort   (jungermannia).      Leafy  part 

s  the  gametophyte  ;  stalk  and  cap-  Four    spores    from       Elaters,  at  left  showing  the  two 

Mile  is  the  sporophyte  (sporogonium  mother    cell    held    in  spiral  marks,  at  right  a  branched 

in  the  bryophytes).  a  group.                            elater. 

Figs.  275-278. — Sporogonium   of  liverwort  (jungermannia)  opening  by  splitting  into  four 
parts,  showing  details  of  elaters  and  spores. 


240 


MORPHOLOG  Y. 


The  Horned  Liverworts.* 

501.  The  horned  liverworts  take  their  name  from  the  shape  of  the  spo- 
rogonium.     This   is   long,  slender,  cylindrical,  pointed,  and   very  slightly 
curved,  suggesting  the  shape  of  a  minute  horn.     Anthoceros  is  one  of  the 
most  common  and  widely  distributed  species.     The  plant  grows  on  damp 
soil  or  on  mud. 

Anthoceros. 

502.  The  gametophyte.—  The  gametophyte  is  thalloid.     It  is  thin,  flat- 
tened, green,  irregularly  ribbon-shaped  and  branched.      It   lies  on  the  soil 

and  is  more  or  less  crisped  or 
wavy,  or  curled,  the  edges  nearly 
plane,  or  somewhat  irregular, 
and  with  minute  lobes,  or 
notches,  especially  near  the 
growing  end.  The  general  form 
and  branching  can  be  seen  in 
fig.  279.  Where  the  plants  are 
much  crowded  the  thallus  is  more 
irregular,  and  often  possesses  nu- 
merous small  lateral  branches  in 
addition  to  the  main  lobes. 
Upon  the  under  side  are  the 
slender  rhizoids,  ^which  attach 
to  the  soil.  With  a  hand  lens 
there  can  be  seen  also  upon  the 
under  side  small  dark,  rounded 
and  thickened  spots,  where  an 
alga  (nostoc)  is  located. 

Sexual  Organs  of 

Anthoceros. 
502.  The  sexual  organs  of  an- 
thoceros  differ  considerably  from 
Anthoceros    gracilis.    A,    several    gameto-  those    of    the    other     liverworts 
phytes,  on  which   sporangia  have  developed; 

B,    an    enlarged    sporogonium,     showing    its  studied.      In  the  first  place  they 
elongated    character   and    dehiscence   by  two  .  ,   .      ,, 

valves,  leaving  exposed  the  slender  columella  are  immersed  in  the  true  tissue 


<.  °f  the  thallus>  Le-  ***  do  not 

(After  Schiffner.)  project  above  the  surface. 

503.  Antheridia.  —  The  antheridium  arises  from  an  internal  cell  of  the 
thallus,  a  cell  just  below  the  upper  surface.     This  cell  develops  usually  a 


*  May  be  used  as  an  alternate  study  for  marchantia. 


HORNED    LIVERWORTS.  24! 

group  of  antheridia  which  lie  in  a  cavity  formed  around  this  cell  as  the 
thallus  continues  to  grow.  They  are  situated  along  the  middle  line  of  the 
thallus,  and  can  be  seen  by  making  a  section  in  this  direction.  The  anthe- 
ridia are  oval  or  rounded, -have  a  wall  of  one  layer  of  cells  which  contains 
the  sperm  cells,  and  each  antheridium  has  a  slender  stalk.  The  sperms 
are  like  those  of  the  true  liverworts. 

504.  Archegonia. — The  archegonia  are  also  borne  along  the  middle  line 
of  the  thallus.     Each  one  arises  at  an  early  stage  in  the  development  of 
the  tissue  of  the  thallus  from  a  superficial  cell,  but  the  archegonium  does 
not  project  above  the  surface.     The  venter  therefore  which   contains  the 
egg  is  deep  down  in  the  thallus,  the  wall  of  the  neck  is  formed  from  cells 
indistinguishable  from  the  adjoining  cells  of  the  thallus  and  opens  at  the 
surface. 

Sporophyte  of  Anthoceros. 

505.  The  Sporogonium. — The  sporogonium  is   developed  from   the  fer- 
tilized egg,  fertilization  resulting  of  course  from  the  fusion  of  one  of  the 
sperms  with  the  nucleus  of  the  egg.     From  the  lower  part  of  the  embryo 
certain  cells  elongate  and  push  out  like  rhizoids  into  the  thallus  (gameto- 
phyte),  but  never  reach  the  outside  so  that  the  sporogonium  derives  its 
nutriment  from  the  gametophyte  in  a  parasitic  manner  like  the  true  liver- 
worts.    It  is  surrounded    at  the  base  by  a  sheath,  an  outgrowth  of  the 
gametophyte. 

506.  Growing  point  of  the  sporogonium. — A  remarkable   thing   about 
the  sporogonium  of  anthoceros,  and  its  relatives,  is  that  the  growing  point 
instead  of  being  situated  at  the  free  end  is  located  near  the  base,  just  above 
the  nourishing  foot.     Thus  the  upper  part  of  the  sporogonium  is  older.     In 
the  old  sporogonia  there  may  be  ripe  spores  near  the  free  end,  young  ones 
near  the  middle,  and  undifferentiated  growing  tissue  near  the  base.     A 
longitudinal  section  of  a  sporogonium  just  as  the  spores  are  ripening  will 
show  this. 

507.  Structure  of  the  sporogonium. — A  longitudinal  section  of  the  spo- 
rogonium shows  that  the  spore-bearing  tissue  occupies  a  comparatively 
small  portion  of  the  sporogonium.     In  the  section  there  is  a  narrow  layer 
(two  cells  thick)  on  either  side   and  joined  at  the  top.     In  the  entire  spo- 
rogonium this  fertile  tissue  is  in  the  shape  of  an  inverted  test-tube  situated 
inside  of  the  sporogonium.     The  wall  of  the  sporogonium  is  about  four 
cells  thick.     The  sterile  tissue  inside  of  the  spore-bearing  tube  is  the  colu- 
mella.     The  cells  of  the  wall  contain  chlorophyll,  and  there  are  true  stomata 
with  guard  cells  in  the  epidermal  layer. 

508.  Spores  and  elaters. — In  the  spore-bearing  tissue  there  are  two  layers 
of  cells  (the  archesporium) .     Each  cell    is  a  potential  mother-cell.     The 
cells,  however,  of  alternate  tiers  do  not  form  spores.     They  elongate  some- 


242  MORPHOLOG  Y. 

what  and  are  romewhat  irregular  and  sometimes  divide  or  branch.  They 
are  supposed  to  represent  rudimentary  elaters.  The  cells  in  the  other  tiers 
are  actual  mother-cells,  and  each  one  forms  four  spores. 

509.  The  sporophyte  of  anthoceros  represents  the  highest  type  found  in 
the  liverworts.     The  spongy  green  parenchyma  forming  the  wall,  with  the 
stomata  in  the  epidermal  layer,  fits  this  tissue  for  the  process  of  photosyn- 
thesis, so  that  this  part  of  the  sporophyte  functions  as  the  green  leaf  of  the 
seed  plants.     It  has  been  suggested  by  some  that  if  the  rhizoids  on  the 
nourishing  foot  could  only  extend  outside  and  anchor  in  the  soil,  the  sporo- 
phyte of  anthoceros  could  live  an  independent  existence.     But  we  see  that 
it  stops  short  of  that. 

Classification   of  the  Liverworts. 

CLASS  HEPATIC.E. 

510.  Order    Marchantiales.* — There    are    two    families    represented    in 
the  United  States. 

Family  Ricciaceae,  including  Riccia  and  Ricciocarpus. 
Family    Marchantiaceae,     including    Marchantia,     Fegatella     (=Cono- 
cephalus),  Fimbriaria,  Targionia,  etc. 

511.  Order  Jungermanniales.* — There  are  two  subdivisions  of  this  order. 
The    AnacrogyncB    include    chiefly    thalloid    forms  with   continued    apical 
growth,  the  archegonia  back  of  the  apical  cell.     Examples:  Blasia,  Aneura, 
Pellia,  etc. 

The  Acrogyna  include  chiefly  foliose  forms,  the  archegonia  arising  from 
the  apical  cell  and  in  such  cases  interrupting  apical  growth.  Examples: 
Cephalozia,  Frullania,  Bazzania,  Jungermannia,  Ptilidium,  Porella,  etc. 

CLASS   ANTHOCEROTES 

512.  The  Anthocerotes  have  formerly  been  placed  with  the  Hepaticaa 
as  an  order.     But  because  of  their  wide  divergence  from  the  other  liver- 
worts in  the  development  of  the  sexual  organs,  and  especially  in  the  struc- 
ture of  the  sporophyte,  they  are  now  by  some  separated  as  a  distinct  class. 
There  is  one  order. 

Order  Anthocerotales* — This  includes  one  family  (Anthocerotacese) 
with  Anthoceros  and  Notothylas  in  Europe  and  North  America,  and  Den- 
droceros  in  the  tropics.  The  latter  is  epiphytic. 


*  As  subclass  in  Engler  and  Prantl. 


CHAPTER  XXV. 

MOSSES    (MUSCI). 

513.  We  are  now  ready  to  take  up  the  more  careful  study  of 
the  moss  plant.     There  are  a  great  many  kinds  of  mosses,  and 
they  differ  greatly  from  each  other  in  the  finer  details  of  struc- 
ture.    Yet  there  are  certain  general  resemblances  which  make  it 
convenient  to  take  for  study  almost  any  one  of  the   common 
species  in  a  neighborhood,  which  forms  abundant  fruit.      Some, 
however,  are  more  suited  to  a  first  study  than  others.      (Polytri- 
chum  and  funaria  are  good  mosses  to  study.) 

514.  Mnium. — We  will  select  here  the  plant  shown  in  fig.  280. 
This  is  known  as  a  mnium  (M.  affine),  and  one  or  another  of  the 
species    of  mnium    can    be    obtained  without    much    difficulty. 
The    mosses,  as    we    have    already    learned,    possess    an    axis 
(stem)  and  leaf-like  expansions^  so  that  they  are  leafy-stemmed 
plants  also.      Certain  of  the  branches  of  the  mnium  stand  upright, 
or  nearly  so,  and  the  leaves  are  all  of  the  same  size  at  any  given 
point  on  the  stem,  as  seen  in  the  figure.     There  are  three  rows 
of  these  leaves,  and  this  is  true  of  most  of  the  mosses. 

515.  The  mnium  plants  usually  form  quite  extensive  and  pretty* 
mats  of  green  in  shady  moist  woods  or  ravines.     Here  and  there 
among  the  erect  stems  are  prostrate  ones,  with  two  rows  of  promi- 
nent leaves  so  arranged  that  it  reminds  one  of  some  of  the  leafy- 
stemmed  liverworts.      If  we  examine  some  of  the  leaves  of  the 
mnium  we  see   that   the   greater  part  of  the  leaf  consists  of  a 
single  layer  of  green  cells,  just  as  is  the  case  in  the  leafy -stemmed 
liverworts.      But  along  the  middle  line  is  a  thicker  layer,  so  that 
it  forme  a  distinct  midrib.     This  ir  characteristic  of  the  leaves 

243 


244 


MORPHOLOGY, 


of  mosses,  and  is  one  way  in  which  they  are  separated  from  the 
leafy-stemmed  liverworts,  the  latter  never  having  a  midrib. 

516.  The  fruiting  moss  plant. — In  fig.  280  is  a  moss  plant  "in 
fruit,"  as  we  say.     Above  the  leafy  stem  a  slender  stalk  bears 


the  capsule,  and  in  this  capsule  are  borne 
the  spores.  The  capsule  then  belongs  to 
the  sporophyte  phase  of  the  moss  plant,  and 
we  should  inquire  whether  the  entire  plant 
as  we  see  it  here  is  the  sporophyte,  or 
whether  part  of  it  is  gametophyte.  If 
a  part  of  it  is  gametophyte  and  a  part 
sporophyte,  then  where  does  the  one  end 
and  the  other  begin  ?  If  we  strip  off  the 
leaves  at  the  end  of  the  leafy  stem,  and 
make  a  longisection  in  the  middle  line,  we 
should  find  that  the  stalk  which  bears  the 
capsule  is  simply  stuck  into  the  end  of  the 


Fig.  280. 

Portion  of  moss  plant  of  Mnium  affine,  showing  two 
sporogonia  from  one  branch.  Capsule  at  left  has  just  shed 
the  cap  or  operculum  ;  capsule  at  right  is  shedding  spores, 
and  the  teeth  are  bristling  at  the  mouth.  Next  to  the  right 
is  a  young  capsule  with  calyptra  still  attached ;  next  are 
two  spores  enlarged. 


leafy  stem,  and  is  not  organically  connected  with  it.  This  is 
the  dividing  line,  then,  between  the  gametophyte  and  the  sporo- 
phyte. We  shall  find  that  here  the  archegonium  containing 


MOSSES. 


245 


the  egg  is  borne,  which  is  a  surer  way  of  determining  the  limits 

of  the  two  phases  of  the  plant. 
» 

517.  The  male  and  female  moss  plants. — The  two  plants  of  mnium  shown  in 

figs.  281,  282  are  quite  different,  as  one  can  easily  see,  and  yet  they  belong 
to  the  same  species.     One  is  a  female  plant,  while  the  other  is  a  male  plant. 

The  sexual  organs  then  in  mnium,  as 
in  many  others  of  the  mosses,  are  borne 
on  separate  plants.  The  archegonia 
are  borne  at  the  end  of  the  stem,  and  are 
protected  by  somewhat  narrower  leaves 
which  closely  overlap  and  are  wrapped 
together.  They  are  similar  to  the 
archegonia  of  the  liverworts. 


Fig.  281. 

Female  plant  (gametophyte)  of  a  moss 
(mnium),  snowing  rhizoids  below,  and  the 
tuft  of  leaves  above  which  protect  the  arche- 
gonia. 


Fig.  282. 


Male    plant    (gametophyte)    of 

aids  below  and  the 


t    -    -  a    moss 

(mnium)  showing  rhizoi 
antheridia  at  the  center  above  surrounded  by 
the  rosette  of  leaves. 


The  male  plants  of  mnium  are  easily  selected,  since  the  leaves  at  the  end 
of  the  stem  form  a  broad  rosette  with  the  antheridia,  and  some  sterile  threads 
packed  closely  together  in  the  center.  The  ends  of  the  mass  of  antheridia 
can  be  seen  with  the  naked  eye,  as  shown  in  fig.  282.  When  the  antheridia 


246 


MORPHOLOG  Y. 


are  ripe,  if  we  make  a  section  through  a  cluster,  or  if  we  merely  tease  out 
some  from  the  end  with  a  needle  in  a  drop  of  water  on  the  slide,  then  prepare 
for  examination  with  the  microscope,  we  can  see  the  form  of  the  antheridia. 
They  are  somewhat  clavate  or  elliptical  in  outline,  as  seen  in  fig.  284.  Be- 
tween them  there  stand  short  threads  composed  of  several  cells  containing 
chlorophyll  grains.  These  are  sterile  threads  (paraphyses). 

518.  Sporogonium. — In  fig.  280  we  see  illustrated  a  sporogonium  of  mnium, 
which  is  of  course  developed  from  the  fertilized  egg  cell  of  the  archegonium. 
There  is  a  nearly  cylindrical  capsule,  bent  downward,  and  supported  on  a  long 


Fig.  284. 

Fig.  283.  Antheridium  of  mnium 

Section  through  end  of  stem  of  female  plant  of  mnium,  show-  with  jointed  paraphysis 
ing  archegonia  at  the  center.  One  archegonium  shows  the  egg.  at  the  left ;  spermato- 
On  the  sides  are  sections  of  the  protecting  leaves.  zoids  at  the  right. 

slender  stalk.  Upon  the  capsule  is  a  peculiar  cap,*  shaped  like  a  ladle  or 
spatula.  This  is  the  remnant  of  the  old  archegonium,  which,  for  a  time  sur- 
rounded and  protected  the  young  embryo  of  the  sporogonium,  just  as  takes 
place  in  the  liverworts.  In  most  of  the  mosses  this  old  remnant  of  the  arche- 
gonium is  borne  aloft  on  the  capsule  as  a  cap,  while  in  the  liverworts  it  is 
thrown  to  one  side  as  the  sporogonium  elongates. 
519.  Structure  of  the  moss  capsule. — At  the  free  end  on  the  moss  capsule 


*  Called  the  calyptra. 


MOSSES. 


247 


as  shown  in  the  case  of  mnium  in  fig.  280,  after  the  remnant  of  the  arche- 
gonium  falls  away,  there  is  seen  a  conical  lid  which  fits  closely  over  the  end. 
When  the  capsule  is  ripe  this  lid  easily  falls  away,  and  can  be  brushed  off 
so  that  it  is  necessary  to  handle  the  plants  with  care  if  it  is 
desired  to  preserve  this  for  study. 

520.   When  the  lid  is  brushed  away  as  the  capsule  dries 
more  we  see  that  the  end  of  the  capsule  covered  by  the  lid 
appears  "  frazzled."     If  we  examine  this  end  with  the  micro- 
scope we    see    that  the  tissue  of   the    capsule    here    is  torn 
with  great  regularity,  so  that  there  are  two  rows  of  narrow, 
sharp  teeth  which    project   outward    in  a  ring    around  the 
opening.     If  we  blow  our  "breath"  upon  these  teeth  they 
will  be  seen  to  move,  and  as  the 
moisture  disappears  and  reappears 
in  the  teeth,  they  close  and  open 
the  mouth  of  the  capsule,  so  sensi- 
tive are  they  to  the  changes  in  the 
humidity  of  the  air.     In  this  way 
all  of  the  spores  are  prevented  to 
some   extent   from  escaping   from 
the  capsule  at  one  time. 

521.  Note.  If  we  make  a  sec- 
tion longitudinal  of  the  capsule  of 
mnium,  or  some  other  moss,  we  find 
that  the  tissue  which  develops  the 
spores  is  much  more  restricted 
than  in  the  capsule  of  the  liver- 
worts which  we  have  studied.  The 
spore -bearing  tissue  is  confined  to\ 
a  single  layer  which  extends  around 
the  capsule  some  distance  from  the 
outside  of  the  wall,  so  that  a  central 

Two  different  stages  of  young  sporogonium  of  cylinder  is  left  of  sterile  tissue. 
a  moss,  still  within  the  archegonhim  and  wedg-  This  is  the  columella,  and  is  pres- 
ing  their  way  into  the  tissue  of  the  end  of  the  stem.  r 

k,  neck  of  archegonium ;  /,  young  sporogonium.  ent  in  nearly  all  the  mosses.     Each 
This  shows  well  the  connection  of  the  sporophyte     -     .  „        r      .        r     ,.,      , 

with  the  gametophyte.  of  the   cells   of    the   fertile   layer 

divides  into  four  spores. 

522.  Development  of  the  sporogonium. — The  egg  cell  after  fertilization 
divides  by  a  wall  crosswise  to  the  axis  of  the  archegonium.  Each  of  these 
cells  continues  to  divide  for  a  time,  so  that  a  cylinder  pointed  at  both  ends  is 
formed.  The  lower  end  of  this  cylinder  of  tissue  wedges  its  way  down 
through  the  base  of  the  archegonium  into  the  tissue  of  the  end  of  the  moss 
stem  as  shown  in  fig.  285.  This  forms  the  foot  through  which  the  nutrient 


Fig.  285. 


248  MORPHOLOGY. 

materials  are  passed  from  the  gametophyte  to  the  sporogonium.  The  upper 
part  continues  to  grow,  and  finally  the  upper  end  differentiates  into  the  mature 
capsule. 

523.  Protonema  of  the  moss. — When  the  spores  of  a  moss  germinate  they 
form  a  thread-like  body,  with  chlorophyll.     This  thread  becomes  branched, 
and  sometimes  quite  extended  tangles  of  these  threads  are  formed.     This  is 
called  the  protonema,  that  \a>  first  thread.     The  older  threads  become  finally 
brown,  while  the  later  ones  are  green.     From  this  protonema   at   certain 
points  buds  appear  which  divide  by  close  oblique  walls.     From  these  buds 
the  leafy  stem  of  the  moss  plant  grows.     Threads  similar  to  these  protonemal 
threads  now  grow  out  from  the  leafy  stem,   to  form  the  rhizoids.     These 
supply  the  moss  plant  with  nutriment,  and  now  the  protonema  usually  dies, 
though  in  some  few  species  it  persists  for  long  periods. 

Classification  of  the  Mosses. 

CLASS  MUSCINEJE   (MUSCI). 

524.  Order  Sphagnales.* — This  order  includes  the  peat  mosses.     There 
is  but  one  family  (Sphagnaceae)  and  but  a  single  genus  (Sphagnum).     The 
peat  mosses  are  widely  distributed  over  the  globe,   chiefly  occurring  in 
moors,  or  "bogs,"  usually  low  ground  around  the  shores  of  lakes,  ponds,  or 
along  streams,  but  they  often  occur  on  wet  dripping  rocks  in  cool  shady 
places.     Small   ponds   are   sometimes  filled  in  by  their  growth.     As  the 
sphagnum  growing  in  such  an  abundance  of  water  only  partially  decays, 
"ground"  is  built  up  rather  rapidly,  and  the  sphagnum  remains  are  known 
as  "peat."     This  "ground "-building  peculiarity  of  sphagnum  sometimes 
enables  the  plant  (often  in  conjunction  with  others)  to  fill  in  ponds  com- 
pletely.    (See  Atoll  Moor,  Chapter  LV.) 

The  gametophyte  of  sphagnum,  like  that  of  all  the  mosses,  is  dimorphic, 
but  the  first  part  (or  protonema)  which  develops  from  the  spores  is  thalloid, 
and  therefore  more  like  the  thallose  liverworts.  The  leafy  axis  (or  gameto- 
phore)  which  develops  from  the  thalloid  form  is  very  characteristic  (see 
Chapter  LV). 

The  archegonia  are  borne  on  the  free  end  of  the  main  axis,  while  the 
antheridia  are  borne  on  short  branches  which  are  brightly  colored,  red, 
yellow,  etc.  The  sporophyte  (sporogonium)  is  globose  and  possesses  a 
broad  foot  anchored  in  the  end  of  a  naked  prolongation  of  the  end  of  the 
leafy  gametophore.  This  naked  prolongation  of  the  gametophore  looks 
like  the  stalk  of  the  sporogonium,  but  a  study  of  its  connection  with  the 
sporogonium  shows  that  it  is  part  of  the  gametophyte,  which  is  only  devel- 
oped after  the  fertilization  of  the  egg  in  the  archegonium.  In  the  sporogo- 
nium there  is  a  short  columella,  and  the  archesporium  is  in  the  form  01  un 
inverted  cup. 


*  As  subclass  in  Engler  and  Prantl. 


MOSSES.  249 

525.  Order  Andreaeales.* — This  order  includes  the  single  genus  An- 
dreaea.     The  plants  are  small  but  form  extensive  mats,  growing  on  rocks 
in  arctic  or  alpine  regions  usually.      They  are  sometimes  found  in  great 
abundance  on  bare,  rather  dry  rocks  on  mountains.     The  protonema  is 
somewhat  thalloid.     The  sporogonium  opens  by  splitting  longitudinally  into 
four  valves.     An  elongated  columella  is  present  so  that  the  archesporium 
is  shaped  like  an  inverted  test-tube. 

526.  Order  Archidiales.* — This  order  contains  the  single  genus  Archi- 
dium,  and  by  some  is  placed  as  an  aberrant  genus  in  the  Bryales.     There 
is  no  columella  in  the  simple  sporogonium.     The  archesporium  occupies 
all  the  internal  part  of  the  sporogonium,  some  cells  being  fertile  and  others 
sterile. 

527.  Order  Bryales.* — These  include  the  higher  mosses,  and  a  very  large 
number  of  genera  and  species.     The  protonema  is  filamentous  and  branched 
except  in  a  few  forms  where  it  is  partly  thalloid  as  in  Tetraphis  (=  Georgia). 
(Tetraphis    pellucida    is    a    common    moss    on    very   rotten   logs.      The 
capsule  has  four  prominent  teeth.)     In  a  few  of  the  lower  genera  (Phas- 
cum,  Pleuridium,  etc.)  the  capsule  opens  irregularly,  but  in  the  larger  num- 
ber the  capsule  opens  by  a  lid  (operculum).     A  cylindrical  columella  is 
present,  and  the  archesporium  is  in  the  form  of  a  tube  open  at  both  ends. 
(Examples:  Polytrichum,  Bryum,  Mnium,  Hypnum,  etc.) 


*  As  subclass  in  Engler  and  Prantl. 


250 


MORPHOLOG  Y. 


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i 


CHAPTER   XXVI. 

FERNS. 

529.  In  taking  up  the  study  of  the  ferns  we  find  plants  which 
are  very  beautiful  objects  of  nature  and  thus  have  always  attracted 
the  interest  of  those  who  love  the  beauties  of  nature.     But  they 
are  also  very  interesting  to   the  student,  because  of  certain  re- 
markable peculiarities  of  the  structure  of  the  fruit  bodies,  and 
especially  because  of  the  intermediate  position  which  they  occupy 
within   the  plant   kingdom,  representing  in  the  two  phases  of 
their  development  the   primitive  type  of  plant  life  on  the  one 
hand,  and  on   the  other  the  modern  type.     We  will  begin  our 
study  of  the  ferns  by  taking  that  form  which  is  the  more  promi- 
nent, the  fern  plant  itself. 

530.  The  Christmas  fern. — One  of  the  ferns  which  is  very 
common  in  the  Northern  States,  and  occurs  in  rocky  banks  and 
woods,  is  the  well-known  Christmas  fern  (Aspidiumacrostichoides) 
shown  in  fig.  286.      The  leaves  are  the  most  prominent  part  of  the 
plant,  as  is  the  case  with  most  if  not  all  our  native  ferns.     The 
stem  is  very  short  and  for  the  most  part  under  the  surface  of  the 
ground,  while  the  leaves  arise  very  close  together,  and  thus  form 
a  rosette  as  they  rise  and  gracefully  bend  outward.      The  leaf  is 
elongate  and  reminds  one  somewhat  of  a  plume  with  the  pinnae 
extending  in  two  rows  on  opposite  sides  of  the  midrib.     These 
pinnae  alternate  with  one  another,  and  at  the  base  of  each  pinna 
is  a  little  spur  which    projects   upward  from  the  upper  edge. 
Such  a  leaf  is  said  to  be  pinnate.     While  all  the  leaves  have  the 
same  general  outline,  we  notice  that  certain  ones,  especially  those 
toward  the  center  of  the  rosette,  are  much  narrower  from  the 

251 


252 


MORPHOLOG  Y. 


middle  portion  toward  the  end.       This  is  because  of  the  shorter 
pinnae  here. 

531.  Fruit  "dots"  (sorus,  indusium) . — If  we  examine  the 
under  side  of  such  short  pinnae  of  the  Christmas  fern  we  see  that 
there  are  two  rows  of  small  circular  dots,  one  row  on  either  side  of 
the  pinna.  These  are  called  the  "  fruit 
dots,"  or  sori  (a  single  one  is  a  sorus).  If 
we  examine  it  with  a  low  power  of  the  mi- 
croscope, 
or  with  a 
p  o  c  k  e  t 
lens,  we 
see  that 
there  is  a 
ci  rcular 
disk  which 
c  o  v  e  r  s 
more  or 


less  com- 
pletelyvery 
minute  objects, usual- 
ly the  ends  of  the 
latter  projecting  just  be- 
yond the  edge  if  they  are 
mature.  This  circular  disk 
is  what  is  called  the  indu- 
sium, and  it  is  a  special 
outgrowth  of  the  epidermis 
of  the  leaf  here  for  the 
protection  of  the  spore- 
cases.  These  minute  ob- 
jects underneath  are  the 
fruit  bodies,  which  in  the 
case  of  the  ferns  and  their  allies  are  called  sporangia.  This 
indusium  in  the  case  of  the  Christmas  fern,  and  also  in  some 
others,  is  attached  to  the  leaf  by  means  of  a  short  slender  stalk 


Fig.  286. 
Christmas  fern  (Aspidium  acrostichoides). 


FEXNS. 


253 


which  is  fastened  to  the  middle  of  the  under  side  of  this  shield, 

as  seen  in  cross  section  in  fig.   292. 

532.  Sporangia.— If  we  section  through  the  leaf  at  one  of  the 

fruit  dots,  or  if  we  tease  off  some  of  the  sporangia  so  that  the 

stalks  are  still  attached,  and 
examine  them  with  the  mi- 
croscope, we  can  see  the 
form  and  structure  of  these 
peculiar  bodies.  Different 
views  of  a  sporangium  are 
shown  in  fig.  293.  The 
slender  portion  is  the  stalk, 
and  the  larger  part  is  the 
spore-case  proper.  We 
should  examine  the  structure 
of  this  spore-case  quite  care- 
fully, since  it  will  help  us  to 
understand  better  than  we 
otherwise  could  the  remark- 
able operations  which  it 
performs  in  scattering  the 
spores. 

533.  Structure  of  a  spo- 
rangium. —  If  we  examine 
one  of  the  sporangia  in  side 
view  as  shown  in  fig.    293, 
Fig  287.  we  note  a  prominent  row  of 

Rhizome  with  bases  of  leaves,  and  roots  of  the  cells    which    extend    around 
Christmas  fern. 

the    margin    of   the    dorsal 

edge  from  near  the  attachment  of  the  stalk  to  the  upper  front 
angle.  The  cells  are  prominent  because  of  the  thick  inner 
walls,  and  the  thick  radial  walls  which  are  perpendicular  to  the 
inner  walls.  The  walls  on  the  back  of  this  row  and  on  its 
sides  are  very  thin  and  membranous.  We  should  make  this 
out  carefully,  for  the  structure  of  these  cells  is  especially  adapt- 
ed to  a  special  function  which  they  perform.  This  row  of  cells 


254  MORPHOLOGY. 

is  termed  the  annulus,  which  means  a  little  ring.  While  this 
is  not  a  complete  ring,  in  some  other  ferns  the  ring  is  nearly 
complete. 

534.     In  the  front  of  the  sporangium  is  another  peculiar  group 


Fig.  288. 
Rhizome  of  sensitive  fern  (Onoclea  sensibilis). 

of  cells.  Two  of  the  longer  ones  resemble  the  lips  of  some  crea- 
ture, and  since  the  sporangium  opens  between  them  they  are 
sometimes  termed  the  lip  cells.  These  lip  cells  are  connected  with 
the  upper  end  of  the  annulus  on  one 
side  and  with  the  upper  end  of  the  stalk 
on  the  other  side  by  thin-walled  cells, 
which  may  be  termed  connective  cells, 
since  they  hold  each  lip  cell  to  its  part 
of  the  opening  sporangium.  The  cells 
on  the  side  of  the  sporangium  are  also 
thin -walled.  If  we  now  examine  a 
sporangium  from  the  back,  or  dorsal 

Fig.  289.  . 

Under  side  of  pinna  of  Aspidium  edge  as  we  say,  it  will  appear  as  in  the 

spinulosum    showing     fruit    dots    .     r    .          j      o  TT 

(Ion).  left-hand    figure.       Here    we    can    see 

how  very  prominent  the  annulus  is.  It  projects  beyond  the 
surface  of  the  other  cells  of  the  sporangium.  The  spores  are 
contained  inside  this  case. 


FERNS. 


255 


535.  Opening  of  the  sporangium  and  dispersion  of  the 
spores. — If  we  take  some  fresh  fruiting  leaves  of  the  Christmas 
fern,  or  of  any  one  of  many  of  the  species  of  the  true  ferns  just 
at  the  ripening  of  the  spores,  and  place  a  portion  of  it  on  apiece 
of  white  paper  in  a  dry  room,  in  a  very  short  time  we  shall  see 
that  the  paper  is  being  dusted  with  minute  brown  objects  which 
fly  out  from  the  leaf.  Now  if  we  take  a  portion  of  the  same 
leaf  and  place  it  under  the  low  power  of  the  microscope,  so  that 
the  full  rounded  sporangia  can  be  seen,  in  a  short  time  we  note 
that  the  sporangium  opens,  the  upper  half  curls  backward  as 


Fig.  290. 
Four  pinnae  of  adiantum,  showing  recurved  margins  which  cover  the  sporangia. 

shown  in  fig.  294,  and  soon  it  snaps  quickly,  to  near  its  former 
position,  and  the  spores  are  at  the  same  time  thrown  for  a  consid- 
erable distance.  This  movement  can  sometimes  be  seen  with  the 
aid  of  a  good  hand  lens. 

536.  How  does  this  opening  and  snapping  of  the  sporan- 
gium take  place  ? — We  are  now  more  curious  than  ever  to  see 
just  how  this  opening  and  snapping  of  the  sporangium  takes  place. 
We  should  now  mount  some  of  the  fresh  sporangia  in  water  and 
cover  with  a  cover  glass  for  microscopic  examination.  A  drop 
of  glycerine  should  be  placed  at  one  side  of  the  cover  glass  on  the 
slip  so  that  the  edge  of  the  glycerine  will  come  in  touch  with  the 
water.  Now  as  one  looks  through  the  microscope  to  watch  the 


256 


MORPHOLOG  Y. 


sporangia,  the  water  should  be  drawn  from  under  the  cover  glass 
with  the  aid  of  some  bibulous  paper,  like  filter  paper,  placed  at  the 

edge  of  the  cover  glass  on 
the  opposite  side  from  the 
glycerine.  As  the  glycer- 
ine takes  the  place  of  the 
water  around  the  sporangia 
it  draws  the  water  out  of 
the  cells  of  the  annulus, 
just  as  it  took  the  water 
out  of  the  cells  of  the 
spirogyra  as  we  learned 
some  time  ago.  As  the 
water  is  drawn  out  of  these 
cells  there  is  produced  a 
pressure  from  without,  the 
atmospheric  pressure  upon 
the  glycerine.  This  causes 
the  walls  of  these  cells  of 
the  annulus  to  bend  in- 
ward, because,  as  we  have 
already  learned,  the  glycer- 

oCS    not  paSS    through 
uugn 

waljs     nearly     SO     fast 

as  the  water  comes  out. 

537.  Now  the  structure  of  the  cells  of  this  annulus,  as  we 
have  seen,  is  such  that  the  inner  walls  and  the  perpendicular 


Fig.  29i. 

Section    through    sorus    of  Polypodium  vulgare    jne 
showing  different  stages  of  sporangium,  and  one 
multicellular  capitate  hair.  faQ 


Fig.  292. 
Section  through  sorus  and  shield-sliaped  indusium  of  aspidium. 

walls  are  stout,  and  consequently  they  do  not  bend  or  collapse 
when  this  pressure  is  brought  to  bear  on  the  outside  of  the  cells. 


FERN'S. 


The  thin  membranous  walls  on  the  back  (dorsal  walls)  and  on 
the  sides  of  the  annulus,  however,  yield  readily  to  the  pressure 
and  bend  inward.  This,  as  we  can  readily  see,  pulls  on  the  ends 
of  each  of  the  perpendicular  walls  drawing  them  closer  together. 
This  shortens  the  outer  surface  of  the  annulus  and  causes  it  to 
first  assume  a  nearly  straight  position,  then  curve  backward  until 
it  quite  or  nearly  becomes  doubled  on  itself.  The  sporangium 


Fig.  203. 
Rear,  side,  and  front  views  of  fern  sporangium.     </,  e,  annulus;  a,  lip  cells. 

opens  between  the  lip  cells  on  the  front  and  the  lateral  walls  of 
the  sporangium  are  torn  directly  across.  The  greater  mass  of 
spores  are  thus  held  in  the  upper  end  of  the  open  sporangium, 
and  when  the  annulus  has  nearly  doubled  on  itself  it  suddenly 
snaps  back  again  in  position.  While  treating  with  the  glycerine 
we  can  see  all  this  movement  take  place.  Each  cell  of  the 
annulus  acts  independently,  but  often  they  all  act  in  concert. 
When  they  do  not  all  act  in  concert,  some  of  them  snap  sooner 
than  others,  and  this  causes  the  annulus  to  snap  in  segments. 

538.   The  movements  of  the  sporangium  can  take  place  in 
old  and  dried  material. — If  we  have  no  fresh  material  to  study 


258 


MORPHOLOG  Y. 


the  sporangium  with,  we  can  use  dried  material,  for  the  move- 
ments of  the  sporangia  can  be  well  seen  in  dried  material,  pro- 
vided it  was  collected  at  about  the  time  the  sporangia  are  mature, 
that  is  at  maturity,  or  soon  afterward.  We  take  some  of  the 
dry  sporangia  (or  we  may  wash  the  glycerine  off  those  which  we 
have  just  studied)  and  mount  them  in  water,  and  quickly  examine 


c^T  o5^ 

w  &    r-e&huii."' 


^^^-f^-r^^Ss^^^  '^  v  ^ 

^3^^^^^5gt 


Fig.  294. 

Dispersion  of  spores  from  sporangium   of  Aspidium  acrostichoides,   showing  different 
stages  in  the  opening  and  snapping  of  the  annulus. 

them  with  a  microscope.  We  notice  that  in  each  cell  of  the 
annulus  there  is  a  small  sphere  of  some  gas.  The  water  which 
bathes  the  walls  of  the  annulus  is  absorbed  by  some  substance 
inside  these  cells.  This  we  can  see  because  of  the  fact  that  this 
sphere  of  gas  becomes  smaller  and  smaller  until  it  is  only  a  mere 


FEXNS.  259 

dot,  when  it  disappears  in  a  twinkling.  The  water  has  been  taken 
in  under  such  pressure  that  it  has  absorbed  all  the  gas,  and  the 
farther  pressure  in  most  cases  closes  the  partly  opened  sporangium 
more  completely. 

539.  Now  we  should  add  glycerine  again  and  draw  out  the 
water,  watching  the  sporangia  at  the  same  time.      We  see  that 
the  sporangia  which  have  opened  and  snapped  once  will  do  it 
again.      And  so  they  may  be  made  to  go  through  this  operation 
several  times  in  succession.     We  should  now  note  carefully  the 
annulus,  that  is  after  the  sporangia  have  opened  by  the  use  of 
glycerine.    So  soon  as  they  have  snapped  in  the  glycerine  we  can 
see  those  minute  spheres  of  gas  again,  and  since  there  was  no  air 
on  the  outside  of  the  sporangia,  but  only  glycerine,  this  gas  must, 
it  is  reasoned,  have  been  given  up  by  the  water  before  it  was  all 
drawn  out  of  the  cells. 

540.  The  common  polypody. — We  may  now  take  up  a  few  other  ferns  for 
study.     Another  common  fern  is  the  polypody,  one  or  more  species  of  which 
have  a  very  wide  distribution.     The  stem  of  this  fern  is  also  not  usually  seen, 
but  is  covered  with  the  leaves,  except  in  the  case  of  those  species  which  grow 
on  the  surface  of  rocks.     The  stem  is  slender  and  prostrate,  and  is  covered 
with  numerous  brown  scales.    The  leaves  are  pinnate  in  this  fern  also,  but  we 
find  no   difference  between  the  fertile  and  sterile  leaves  (except  in  some  rare 
cases).    The  fruit-dots  occupy  much  the  same  positions  on  the  under  side  of  the 
leaf  that  they  do  in  the  Christmas  fern,  but  we  cannot  find  any  in,dusium.     In 
the  place  of  an  indusium  are  club-shaped  hairs  as  shown  in  fig.  291.    The  en- 
larged ends  of  these  clubs  reaching  beyond  the  sporangia  give  some  protection 
to  them  when  they  are  young. 

541.  Other  ferns. — We  might  examine  a  series  of  ferns  to  see  how  different 
they  are  in  respect  to  the  position  which  the  fruit  dots  occupy  on  the  leaf.    The 
common  brake,  which  sometimes  covers  extensive  areas  and  becomes  a  trouble- 
some weed,  has  a  stout  and  smooth  underground  stem  (rhizome)  which  is  often 
12  to  20  cm  beneath  the  surface  of  the  soil.     There  is  a  long  leaf  stalk,  which 
bears  the  lamina,  the  latter  being  several  times  pinnate.     The  margins  of  the 
fertile  pinnae  are  inrolled,  and  the  sporangia  are  found  protected  underneath 
in  this  long  sorus  along  the  margin  of  the  pinna.     The  beautiful  maidenhair  fern 
and  its  relatives  have  obovate  pinnae,  and  the  sori  are  situated  in  the  same  posi- 
tions as  in  the  brake.      In  other  ferns,  as  the  walking  fern,  the  sori  are  borne 
along  by  the  side  of  the  veins  of  the  leaf. 

542.  Opening  of  the  leaves  of  ferns. — The  leaves  of  ferns  open  in  a  peculiar 
manner.     The  tip  of  the  leaf  is  the  last  portion  developed,  and  the  growing 


260 


MORPHOLOGY. 


leaf  appears  as  if  it  was  rolled  up  as  in  fig.  287  of  the  Christmas  fern.     As  the 
leaf  elongates  this  portion  unrolls. 

543.  Longevity  of  ferns. — Most  ferns  live  from  year  to  year,  by  growth 
adding  to  the  advance  of  the  stem,  while  by  decay  of  the  older  parts  the  stem 
shortens  up  behind.  The  leaves  are  short-lived,  usually  dying  down  each 
year,  and  a  new  set  arising  from  the  growing  end  of  the  stem.  Often  one  can 
see  just  back  or  below  the  new  leaves  the  old  dead  ones  of  the  past  season, 
and  farther  back  the  remains  of  the  petioles  of  still  older  leaves. 

544.  Budding  of  ferns.  —  A  few 
ferns  produce  what  are  called  bulbils 
or  bulblets  on  the  leaves.  One  of 
these,  which  is  found  throughout  the 
greater  part  of  the  eastern  United 
States,  is  the  bladder  fern  (Cystop- 
teris  bulbifera),  which  grows  in  shady 
rocky  places.  The  long  graceful 
delicate  leaves  form  in  the  axils  of 
the  pinnae,  especially  near  the  end  of 
the  leaf,  small  oval  bulbs  as  shown 
in  fig.  295.  If  we  examine  one  of 
these  bladder-like  bulbs  we  see  that 
the  bulk  of  it  is  made  up  of  short 
thick  fleshy  leaves,  smaller  ones  ap- 
pearing between  the  outer  ones  at  the 
smaller  end  of  the  bulb.  This  bulb 
contains  a  stem,  young  root,  and 
several  pairs  of  these  fleshy  leaves. 
They  easily  fall  to  the  ground  or 
rocks,  where,  with  the  abundant 
moisture  usually  present  in  localities 

F;  where   the    fern    is   found,  the  bulb 

Cystopteris  bulbifera,  young  plant  growing  grows  until  the  roots  attach  the  plant 

p'nnaoHeaf  At  ^  *  ^^  ^  "*  ^  °f  to  the  soil  or  in  the   crevices   of  the 

rocks.     A  young  plant  growing  from 
one  of  these  bulbils  is  shown  in  fig.  295. 

545.  Greenhouse  ferns. — Some  of  the  ferns  grown  in  conservatories  have 
similar  bulblets.    Fig.  296  represents  one  of  these  which  is  found  abundantly 
on  the  leaves  of  Asplenium  bulbiferum.    These  bulbils  have  leaves  which  are 
very  similar   to    the    ordinary  leaf  except    that    they  are    smaller.      The 
bulbs  are  also  much  more  firmly  attached  to  the  leaf,  so  that  they  do  not 
readily  fall  away. 

546.  Plant  conservatories  usually  furnish  a  number  of  very  interesting 
ferns,  and  one  should  attempt  to  make  the  acquaintance  of  some  of  them,  for 


FEXNS. 


26l 


here  one  has  an  opportunity  during  the  winter  season  not  only  to  observe  these 
interesting  plants,  but  also  to  obtain  material  for  study.  In  the  tree  ferns 
which  often  are  seen  growing  in  such  places  we  see  examples  of  the  massive 
trunks  and  leaves  of  some  of  the  tropical  species. 

547.  The  fern  plant  is  a  sporophyte. — We  have  now  studied 
the  fern  plant,  as  we  call  it,  and  we  have  found  it  to  represent 
the  spore-bearing  phase  of  the  plant,  that  is  the  sporophyte  (cor- 
responding to  the  sporogoniurn  of  the  liverworts  and  mosses). 

548.  Is  there  a  ga- 
metophyte     phase    in 
ferns  ? — But  in  the  spor- 
ophyte of  the  fern,  which 
we  should  not  forget  is 
the  fern  plant,  we  have 
a  striking  advance  upon 
the   sporophyte    of   the 
liverworts   and   mosses. 
In  the  latter  plants  the 
sporophyte       remained 
attached  to  the  gameto- 
phyte,   and  derived  its 
nourishment    from     it. 
In  the  ferns,  as  we  see, 
the    sporophyte    has    a 
root  of  its  own,  and  is 
attached    to    the    soil. 
Through  the  aid  of  root 

hairs  of  its  own  it  takes  up  mineral  solutions.  It  possesses  also 
a  true  stem,  and  true  leaves  in  which  carbon  conversion  takes 
place.  It  is  able  to  live  independently,  then.  Does  a  gametophy te 
phase  exist  among  the  ferns  ?  Or  has  it  been  lost  ?  If  it  does 
exist,  what  is  it  like,  and  where  does  it  grow  ?  From  what  we 
have  already  learned  we  should  expect  to  find  the  gametophyte 
begin  with  the  germination  of  the  spores  which  are  developed 
on  the  sporophyte,  that  is  on  the  fern  plant  itself.  We  should 
investigate  this  and  see. 


Fig.  296. 
Bulbil  growing  from  leaf  of  asplenium  (A ,  bulbiferum). 


CHAPTER    XXVII. 

FERNS    CONTINUED. 
Gametophyte  of  ferns. 

549.  Sexual  stage  of  ferns. — We  now  wish  to  see  what  the 
sexual  stage  of  the  ferns  is  like.  Judging  from  what  we  have 
found  to  take  place  in  the  liverworts  and  mosses  we  should  infer 


Fig.  297. 

Prothallium  of  fern,  under  side,  showing  rhizoids,  antheridia  scattered  among  and  near 
them,  and  the  archegonia  near  the  sinus. 

that  the  form  of  the  plant  which  bears  the  sexual  organs  is  de- 
veloped from  the  spores.  This  is  true,  and  if  we  should  examine 
old  decaying  logs,  or  decaying  wood  in  damp  places  in  the  near 

262 


FERNS. 


vicinity  of  ferns,  we  should  probably  find  tiny,  green,  thin,  heart- 
shaped  growths,  lying  close  to  the  substratum.  These  are  also 
found  quite  frequently  on  the  soil  of  pots  in  plant  conservatories 
where  ferns  are  grown.  Gardeners  also  in  conservatories  usually 
sow  fern  spores  to  raise  new  fern  plants, 
and  usually  one  can  find  these  heart-shaped 
growths  on  the  surface  of  the  soil  where 
they  have  sown  the  spores.  We  may  call 
the  gardener  to  our  aid  in  finding  them  in 
conservatories,  or  even  in  growing  them  for 
us  if  we  cannot  find  them  outside.  In  some 
cases  they  may  be  grown  in  an  ordinary  room 
by  keeping  the  surfaces  where  they  are 
growing  moist,  and  the  air  also  moist,  by 
placing  a  glass  bell  jar  over  them. 

550.  In  fig.  297  is  shown  one  of  these  growths  enlarged. 
Upon  the  under  side  we  see  numerous  thread-like  outgrowths, 
the  rhizoids,  which  attach  the  plant  to  the  substratum,  and  which 
act  as  organs  for  the  absorption  of  nourishment.  The  sexual 

organs  are 
borne  on  the 
under  side  also, 
and  we  will 
study  them 
later.  This 
heart-shaped, 
Fig.  300.  flattened,  thin, 

Spore  crushed  to  remove  exospore  and    green    plant    is 
show  endospore. 

the  prothalhum 


Fig.   298. 

Spore  of  Pteris  serru- 
lata  showing  the  three- 
rayed  elevation  along 
the  side  of  which  the 
spore  wall  cracks  during 
germination. 


Fig.  299. 


Spore  of  Aspidium 
acrostichoides  with 
winged  exospore. 

of  ferns,  and  we  should  now  give  it  more  careful  study,  be- 
ginning with  the  germination  of  the  spores. 

551.  Spores. — We  can  easily  obtain  material  for  the  study  of 
the  spores  of  ferns.  The  spores  vary  in  shape  to  some  extent. 
Many  of  them  are  shaped  like  a  three-sided  pyramid.  One  of 
these  is  shown  in  fig.  298.  The  outer  wall  is  roughened,  and 
on  one  end  are  three  elevated  rid,ges  which  radiate  from  a  given 


264 


MORPHOLOG  Y. 


point.     A  spore  of  the  Christmas  fern  is  shown  in  fig.  299.    The 
outer  wall  here  is  more  or  less  winged.     At  fig.  300  is  a  spore 

of  the  same  species  from  which  the 
outer  wall  has  been  crushed,  showing 
that  there  is  an  inner  wall  also.  If 
possible  we  should  study  the  germi- 
nation of  the  spores  of  some  fern. 

552.  Germination  of  the  spores. 
— After  the  spores  have  been  sown  for 
about  one  week  to  ten  days  we  should 

Fig.  301.  -         .  .. 

Spores  of  asplenium  ;  exospore  re-    mOUnt  a  feW  in  Water  f°r  examination 
moved  from  the  one  at  the  right.  wjth  the  microscope  in  order  to  study 

the  early  stages.     If  germination  has  begun,  we  find  that  here 
and  there  are  short  slender  green  threads,  in  many  cases  attached 

to  brownish  bits,  the  old 
walls  of  the  spores, 
i  Often  one  will  sow  the 
sporangia  along  with  the 
spores,  and  in  such  cases 
there  may  be  found  a 
number  of  spores  still 
within  the  old  sporan- 
gium wall  that  are  ger- 
minating, when  they  will 
appear  as  in  fig.  302. 

553.     Protonema.  — 
These  short  green  threads 
are  called  protonemal  threads,  or  profonema, 
which    means   a  first  thread,   and    it    here 
signifies  that    this   short   thread    only  pre- 
cedes a  larger  growth  of  the  same  object. 
In  figs.  302,  303  are  shown  several  stages  of 
germination  of  different  spores.      Soon  after 
Germinating  Spores    of tne    short    germ    tube    emerges    from    the 
sun  m  the  crack  jn  the  spore  wall,   it  divides  by  the 


FERNS.  265 

formation  of  a  cross  wall,  and  as  it  increases  in  length  other 
cross  walls  are  formed.  But  very  early  in  its  growth  we  see  that 
a  slender  outgrowth  takes  place  from  the  cell  nearest  the  old 
spore  wall.  This  slender  thread 
is  colorless,  and  is  not  divided 
into  cells.  It  is  the  first  rhizoid, 
and  serves  both  as  an  organ  of 
attachment  for  the  thread,  and  for 
taking  up  nutriment. 

554.  Prothallium. — Very  soon, 
if  the   sowing    has    not    been   so 
crowded  as  to  prevent  the  young 
plants    from    obtaining    nutriment 
sufficient,  we  will  see  that  the  end 
of  this  protonema  is  broadening, 
as  shown  in  fig.  303.     This  is  done 
by  the  formation  of  the  cell  walls 
in   different   directions.       It   now 
continues  to  grow  in  this  way,  the 
end  becoming  broader  and  broader, 
and  new  rhizoids  are  formed  from 
the  under  surface  of  the  cells.     The 
growing  point  remains  at  the  mid- 
dle of  the  advancing  margin,  and 
the  cells  which   are   cut  off  from 
either  side,  as   they  become   old, 

widen     out.       In     this    way    the     Youn|f  proth^°oi  a  fern 

"  wings,"     or    margins    of     the  bolus)- 

little,  green,  flattened   body,   are  in   advance  of  the  growing 

point,  and  the  object  is  more  or  less  heart-shaped,  as  shown 

in   fig.  297.         Thus  we  see  how  the  prothallium  of  ferns  is 

formed. 

555.  Sexual  organs  of  ferns. — If  we  take  one  of  the  prothal- 
lia  of  ferns  which  have  grown  from  the  sowings  of  fern  spores, 
or  one  of  those  which  may  be  often  found  growing  on  the  soil 


266 


MORPHOLOG  Y. 


of  pots  in  conservatories,   mount    it   in  water  on  a  slip,   with 
the  under  side  uppermost,   we  can   then   examine    it    for   the 


Fig.  304- 

Male  prothallium  of  a  fern  (niphobolus),  in  form  of  an  alga  or  protonema.     Spermato- 
zoids  escaping  from  antheridia. 

sexual  organs,  for  these  are  borne  in  most  cases  on  the  under 
side. 

556.  Afitheridia. — If  we  search  among  the  rhizoids  we  see 
small    rounded   elevations   as    shown   in   fig.  297   or  305   scat- 


Fig.  305. 

Male  prothallium  of  fern  (niphobolus),  showing  opened  and  unopened  antheridid,  section 
of  unopened  antheridium ;  spermatozoids  escaping ;  spermatozoids  which  did  n^t  escape 
from  the  antheridium. 


FEXNS. 


267 


These  are  the  an- 


tered  over  this  portion  of  the  prothallium. 
theridia.  If  the  pro- 
thallia  have  not  been 
watered  for  a  day  or 
so,  we  may  have  an 
opportunity  of  see- 
ing the  spermato- 
zoids coming  out  of 
the  antheridium,  for 
when  the  prothallia  Fig  306. 

Section  of  anthendia  showing  sperm  cells,  and  spermato- 

are  freshly  placed   in  «>ids  in  the  one  at  the  right. 

water  the  cells  of  the  antheridium  ab- 
sorb water.  This  presses  on  the  con- 
tents of  the  antheridium  and  bursts  the 
cap  cell  if  the  antheridium  is  ripe,  and 
all  the  spermatozoids  are  shot  out. 
We  can  see  here  that  each  one  is 
shaped  like  a  screw,  with  the  coils  at 
But  as  the  spermatozoid 

in      A       ifuict      I   <  (I  IU  I  L  I  I  Ml  -        '"        »v»*Nfvrw» 

(Adiantum  concinnum). 

what  and  by  the  vibration  of 
the  long  cilia  which  are  on  the 
smaller  end  it  whirls  away.  In 
such  preparations  one  may  often 
see  them  spinning  around  for  a 
long  while,  and  it  is  only  when 
they  gradually  come  to  rest 
that  one  can  make  out  their 
form. 

557.  Archegonia. — If  we  now 
examine  closely  on  the  thicker 
part  of  the  under  surface  of  the 
prothallium,    just    back    of  the 
-sinus,"    we    may   see     longer  vent^fteTgg! next  is 
stout  projections  from  the  surface  n^ieUf  the  SnafSl.  °f 
of  the  prothallium.     These  are  shown  in  fig,  297.      They  are 


Fig.  307- 

Different  views  of  spermatozoids;  first    close, 
in  a    quiet   condition;    in    motion 

begins  to  move  this  coil  opens  some- 


268 


MORPHOLOG  Y. 


the  archegonia.     One  of  them  in  longisection  is  shown  in  fig. 
308.      It  is  flask -shaped,  and  the  broader  portion  is  sunk  in  the 


Fig.  309. 

Mature  and  open  archegonium  of  fern  (Adiantum  cuneatum)  with  spermatozoids  making 
their  way  down  through  the  slime  to  the  egg. 

tissue  of  the  prothallium.  The  egg  is  in  the  larger  part.  The 
spermatozoids  when  they  are  swimming 
around  over  the  under  surface  of  the  pro- 
thallium  come  near  the  neck,  and  here  they 
are  caught  in  the  viscid  substance  which 
has  oozed  out  of  the  canal  of  the  arche- 
gonium. From  here  they  slowly  swim 
down  the  canal,  and  finally  one  sinks  into 
the  egg,  fuses  with  the  nucleus  of  the  latter, 
and  the  egg  is  then  fertilized.  It  is  now 
(After  ready  to  grow  and  develop  into  the  fern 

phyte,  which  begins  with  the  fertilized  egg. 


Fig.  310. 


fofntLlg 


nt 

Campbell.) 


Sporophyte. 

558.  Embryo. — The  egg  first  divides  into  two  cells  as  shown  in  fig.  228,  then 
into  four.  Now  from  each  one  of  these  quandrants  of  the  embryo  a  definite 
part  of  the  plant  develops,  from  one  the  first  leaf,  from  one  the  stern,  from 
one  the  root,  and  from  the  other  the  organ  which  is  called  the  foot,  and  which 


269 


attaches  the  embryo  to  the  prothallium,  and  transports  nourishment  for  the 
embryo  until  it  can  become  attached  to  the  soil  and  lead  an  independent  ex- 
istence. During  this  time  the  wall  of  the  archegonium  grows  somewhat  to 
accommodate  the  increase  in  size  of  the  embryo,  as  shown  in  figs.  312,  313. 
But  soon  the  wall  of  the  archegonium  is  ruptured  and  the  embryo  emerges, 
the  root  attaches  itself  to  the  soil,  and  soon  the  prothallium  dies. 

The  embryo  is  first  on  the  under  side  of  the  prothallium,  and  the  first  leaf 


Fig.  3". 
Two-celled  embryo  of  Pteris  serrulata.     Remnant  of  archegonium  neck  below. 

and  the  stem  curves  upward  between  the  lobes  of  the  heart-shaped  body,  and 
then  grows  upright  as  shown  in  fig.  314.  Usually  only  one  embryo  is  formed 
on  a  single  prothallium,  but  in  one  case  I  found  a  prothallium  with  two  well- 
formed  embryos,  which  are  figured  in  315. 

559.  Comparison  of  ferns  with  liverworts  and  mosses. — In  the  ferns  then 
we  have  reached  a  remarkable  condition  of  things  as  compared  with  that 
which  we  found  in  the  mosses  and  liverworts.  In  the  mosses  and  liverworts 


MORPHOLOG  Y. 


the  sexual  phase  of  the  plant  (gametophyte)  was  the  prominent  one, 
and  consisted  of  either  a  thallus  or  a  leafy  axis,  but  in  either  case  it  bore  the 
sexual  organs  and  led  an  independent  existence;  that  is  it  was  capable  of  ob- 
taining its  nourishment  from  the  soil  or  water  by  means  of  organs  of  absorp- 
tion belonging  to  itself,  and  it  also  performed  the  office  of  photosynthesis. 

560.    The  spore-bearing  phase  (sporophyte)  of  the  liverworts  and  mosses, 
on  the  other  hand,  is  quite  small  as  compared  with  the  sexual  stage,  and  it  is 


li 


ft 


Fig.  312. 

Young  embryo  of  fern  (Adiantum  concinnum)  in  enlarged  venter  of  the  archegonium.    S, 
stem  ;  L,  first  leaf  or  cotyledon  ;  Jf,  root ;  F,  foot. 

completely  dependent  on  the  sexual  stage  for  its  nourishment,  remaining  at- 
tached permanently  throughout  all  its  development,  by  means  of  the  organ 
called  a  foot,  and  it  dies  after  the  spores  are  mature. 

561.  Now  in  the  ferns  we  see  several  striking   differences.     In  the  first 
place,  as  we  have  already  observed,  the  spore-bearing  phase  (sporophyte)  of 


FERNS. 


271 


the  plant  is  the  prominent  one,  and  that  which  characterizes  the  plant.  It 
also  leads  an  independent  existence,  and,  with  the  exception  of  a  few  cases, 
does  not  die  after  the  development  of  the  spores,  but  lives  from  year  to  year 
and  develops  successive  crops  of  spores.  There  is  a  distinct  advance  here  in 
the  size,  complexity,  and  permanency  of  this  phase  of  the  plant. 

562.  On  the  other  hand  the  sexual  phase  of  the  ferns  (gametophyte),  while 
it  still  is  capable  of  leading  an  independent  existence,  is  short-lived  (with  very 
few  exceptions).  It  is  also  much  smaller  than  most  of  the  liverworts  and 


Fig.  313. 

Embryo  of  fern  (Adiantum  concinnum)  still  surrounded  by  the  archegonium,  which  has 
grown  in  size,  forming  the  "  calyptra."     L,  leaf ;  S,  stem ;  Jf,  root ;  F,  foot. 

mosses,  especially  as  compared  with  the  size  of  the  spore-bearing  phase. 
The  gametophyte  phase  or  stage  of  the  plants,  then,  is  decreasing  in  size  and 
durance  as  the  sporophyte  stage  is  increasing.  We  shall  be  interested  to  see 
if  this  holds  good  of  the  fern  allies,  that  is  of  the  plants  which  belong  to  the 
same  group  as  the  ferns.  And  as  we  come  later  to  take  up  the  study  of  the 
higher  plants  we  must  bear  in  mind  to  carry  on  this  comparison,  and  see  if 
this  progression  on  the  one  hand  of  the  sporophyte  continues,  and  if  the 
retrogression  of  the  gametophyte  continues  also. 


2/2 


MORPHOLOG  Y. 


Fig.  314- 

Young  plant  of  Pteris  serrulata  still 
attached  to  prothallium. 


Fig.  315. 

Two  embryos  from  one  prothallium  of 
Adiantum  cuneatum. 


CHAPTER  XXVIII. 

DIMORPHISM   OF   FERNS. 

563.  In  comparing  the  different  members  of  the  leaf  series 
there  are  often  striking  illustrations  of  the  transition  from  one 
form  to  another,  as  we  have  noted  in  the  case  of  the  trillium 
flower.      This  occurs  in  many  other  flowers,  and  in  some,  as  in 
the  water  lily,  these  transformations  are   always  present,   here 
showing  a  transition  from  the  petals  to  the  stamens.      In  the  bud 
scales  of  many  plants,  as  in  the  butternut,  walnut,  currant,  etc., 
there  are  striking  gradations  between  the  form  of  the  simple  bud 
scales  and  the  form  of  the  leaf.     Some  of  the  most  interesting  of 
these  transformations  are  found  in  the  dimorphic  ferns. 

564.  Dimorphism  in  the  leaves  of  ferns. — In  the  common 
polypody  fern,  the  maidenhair,  and  in  many  other  ferns,  all  the 
leaves  are  of  the  same  form.     That  is,  there  is  no  difference  be- 
tween the  fertile  leaf  and  the  sterile  leaf.     On  the  other  hand,  in 
the  case   of  the  Christmas  fern  we  have   seen  that   the   fertile 
leaves  are  slightly  different  from  the  sterile  leaves,  the  former 
having  shorter  pinnae  on  the  upper  half  of  the  leaf.     The  fertile 
pinnae  are  here  the  shorter  ones,  and  perform  but  little  of  the 
function  of  carbon   conversion.       This  function  is  chiefly  per- 
formed by  the  sterile  leaves  and  by  the  sterile  portions  of  the 
fertile  leaves.     This  is  a  short  step  toward  the  division  of  labor 
between  the  two  kinds  of  leaves,  one  performing  chiefly  the  labor 
of  carbon  conversion,  the  other  chiefly  the  labor  of  bearing  the 
fruit. 

565.  The  sensitive  fern. — This  division  of  labor  is  carried  to 
an  extreme  extent  in  the  case  of  some  ferns.    Some  of  our  native 

273 


274 


MORPHOLOG  Y. 


ferns  are  examples  of  this  interesting  relation  between  the  leaves 
like  the  common  sensitive  fern  (Onoclea  sensibilis)  and  the 
ostrich  fern  (O.  struthiopteris)  and  the  cinnamon  fern  (Osmimda 
cinnamomea).  The  sensitive  fern  is  here  shown  in  fig.  316. 
The  sterile  leaves  are  large,  broadly  expanded,  and  pinnate,  the 


Fig.  31 6. 
Sensitive  fern ;  normal  condition  of  vegetative  leaves  and  sporophylls. 

pinnae  being  quite  large.  The  fertile  leaves  are  shown  also  in 
the  figure,  and  at  first  one  would  not  take  them  for  leaves  at  all. 
But  if  we  examine  them  carefully  we  see  that  the  general  plan 
of  the  leaf  is  the  same :  the  two  rows  of  pinnae  which  are  here 
much  shorter  than  in  the  sterile  leaf,  and  the  pinnules,  or  smaller 


DIMORPHISM  OF  FERNS. 


275 


divisions  of  the  pinnae,  are  inrolled  into  little  spherical  masses 
which  lie  close  on  the  side  of  the  pinnae.  If  we  unroll  one  of 
these  pinnules  we  find  that  there  are  several  fruit  dots  within 
protected  by  this  roll.  In  fact  when  the  spores  are  mature  these 


Fig.  317- 
Sensitive  fern ;  one  fertile  leaf  nearly  changed  to  vegetative  leaf. 

pinnules  open  somewhat,  so  that  the  spores    may  be    dissemi- 
nated. 

There  is  very  little  green  color  in  these  fertile  leaves,  and 
what  green  surface  there  is  is  very  small  compared  with  that  of 
the  broad  expanse  of  the  sterile  leaves.  So  here  there  is  practi- 
cally a  complete  'division  of  labor  between  these  two  kinds  of 


MORPHOLOGY. 


leaves,  the  general  plan  of  which  is  the  same,  and  we  recognize 
each  as  being  a  leaf. 

566.  Transformation  of  the  fertile  leaves  of  onoclea  to 
sterile  ones. — It  is  not  a  very  rare  thing  to  find  plants  of  the 
sensitive  fern  which  show  intermediate  conditions  of  the  sterile 
and  the  fertile  leaf.  A  number  of  years  ago  it  was  thought  by 
some  that  this  represented  a  different  species,  but  now  it  is  known 


Fig.  318. 
Sensitive  fern,  showing  one  vegetative  leaf  and  two  sporophylls  completely  transformed. 

that  these  intermediate  forms  are  partly  transformed  fertile  leaves. 
It  is  a  very  easy  matter  in  the  case  of  the  sensitive  fern  to  pro- 
duce these  transformations  by  experiment.  If  one  in  the  spring, 
when  the  sterile  leaves  attain  a  height  of  12  to  16  cm  (8-10 
inches),  cuts  them  away,  and  again  when  they  have  a  second 
time  reached  the  same  height,  some  of  the  fruiting  leaves  which 
develop  later  will  be  transformed.  A  few  years  ago  I  cut  off  the 


DIMORPHISM   OF  FERNS. 


277 


sterile  leaves  from  quite  a  large  patch  of  the  sensitive  fern,  once 
in  May,  and  again  in  June.  In  July,  when  the  fertile  leaves 
were  appearing  above  the  ground,  many  of  them  were  changed 
partly  or  completely  into  sterile  leaves.  In  all  some  thirty  plants 


Fig.  3 TO. 
Normal  and  transformed  sporophyll  of  sensitive  fern. 

showed  these  transformations,  so  that  every  conceivable  gradation 
was  obtained  between  the  two  kinds  of  leaves. 

567.  It  is  quite  interesting  to  note  the  form  of  these  changed 
leaves  carefully,  to  see  how  this  change  has  affected  the  pinnae 
and  the  sporangia.  We  note  that  the  tip  of  the  leaf  as  well  as 
the  tips  of  all  the  pinnae  are  more  expanded  than  the  basal  por- 


278  MORPHOLOG  Y. 

tions  of  the  same.  This  is  due  to  the  fact  that  the  tip  of  the 
leaf  develops  later  than  the  basal  portions.  At  the  time  the 
stimulus  to  the  change  in  the  development  of  the  fertile  leaves 
reached  them  they  were  partly  formed,  that  is  the  basal  parts  of 
the  fertile  leaves  were  more  or  less  developed  and  fixed  and 
could  not  change.  Those  portions  of  the  leaf,  however,  which 
were  not  yet  completely  formed,  under  this  stimulus,  or  through 
correlation  of  growth,  are  incited  to  vegetative  growth,  and  ex- 
pand more  or  less  completely  into  vegetative  leaves. 

568.  The  sporangia  decrease  as  the  fertile  leaf  expands. — 
If  we  now  examine  the  sporangia  on  the  successive  pinnae  of  a 
partly  transformed  leaf  we  find  that  in  case  the  lower  pinnae  are 
not  changed  at  all,  the  sporangia  are  normal.      But  as  we  pass  to 
the  pinnae  which  show  increasing  changes,  that  is  those  which  are 
more  and  more  expanded,  we  see  that  the  number  of  sporangia 
decrease,  and   many  of  them  are    sterile,   that  is  they  bear  no 
spores.      Farther  up  there  are  only  rudiments  of  sporangia,  until 
on  the  more  expanded  pinnae  sporangia  are  no  longer  formed, 
but  one  may  still  see  traces  of  the  indusium.      On  some  of  the 
changed  leaves  the  only  evidences  that  the  leaf  began  once  to 
form  a  fertile  leaf  are  the  traces  of  these   indusia.      In  some  of 
these  cases  the  transformed  leaf  was  even  larger  than  the  sterile 
leaf. 

569.  The  ostrich,  fern. — Similar  changes  were  also  produced 
in  the  case  of  the  ostrich  fern,  and  in  fig.  320  is  shown  at  the 
left  a  normal  fertile  leaf,  then  one  partly  changed,  and  at  the 
right  one  completely  transformed. 

570.  Dimorphism  in  tropical  ferns. — Very  interesting  forms 
of  dimorphism  are  seen  in  some  of  the  tropical  ferns.      One  of 
these  is  often  seen  growing  in  plant  conservatories,  and  is  known 
as  the  staghorn   fern  (Platycerium  alcicorne).     This  in  nature 
grows  attached  to  the  trunks  of  quite  large  trees  at  considerable 
elevations  on  the  tree,  sometimes  surrounding  the  tree  with  a 
massive  growth.     One  kind  of  leaf,  which  may  be  either  fertile 
or  sterile,  is  narrow,  arid  branched  in  a  peculiar  manner,  so  that 
it  resembles  somewhat  the  branching    of  the  horn   of  a  stag. 


DIMORPHISM  OF  FERNS. 


2/9 


Below  these  are  other  leaves  which  are  different  in  form  and 
sterile.  These  leaves  are  broad  and  hug  closely  around  the  roots 
and  bases  of  the  other  leaves.  Here  they  serve  to  catch  and 


Fig.  320. 

Ostrich  fern,  showing  one  normal  sporophyll,  one  partly  transformed,  and  one  completely 
transformed. 

retain  moisture,  and  they  also  catch  leaves  and  other  vegetable 
matter  which  falls  from  the  trees.  In  this  position  the  leaves 
decay  and  then  serve  as  food  for  the  fern. 


CHAPTER  XXIX. 

HORSETAILS. 

571.  Among   the    relatives  of  the   ferns   are   the 
horsetails,  so  called  because  of  the  supposed  resem- 
blance of  the  branched  stems  of  some  of  the  species 
to  a  horse's  tail,  as  one  might  infer  from  the  plant 
shown  in  fig.  325.      They  do  not  bear  the  least  re- 
semblance to  the  ferns  which  we   have  been  study- 
ing.    But  then  relationship  in  plants  does  not  depend 
on  mere  resemblance  of  outward  form,  or  of  the  promi- 
nent part  of  the  plant. 

572.  The  field  equisetum.     Fertile  shoots.  —  Fig. 
321   represents  the  common  horsetail  (Equisetum  ar- 
vense).      It  grows  in  moist  sandy  or  gravelly  places, 
and  the  fruiting  portion  of  the  plant  (for  this  species 
is  dimorphic),   that   is  the  portion  which   bears  the 
spores,  appears  above  the  ground  early  in  the  spring. 
It  is  one  of  the  first  things  to  peep  out  of  the  recently 
frozen  ground.     This  fertile  shoot  of  the  plant  does 
not  form    its    growth    this    early  in  the   spring.      Its 
development   takes   place  under   the   ground   in  the 
autumn,  so  that  with  the  advent  of  spring  it  pushes 
up  without   delay.       This   shoot   is   from    10    to    20 
cm    high,    and   at    quite    regular   intervals   there   are 
slight    enlargements,    the    nodes    of  the    stem.     The 
cylindrical    portions    between    the     nodes    are     the 
internodes.     If  we  examine  the  region  of  the  inter-    Portion1*  of 


nodes  carefully  we  note    that   there   are    thin    mem- 
branous  scales,  more  or  less  triangular  in  outline,  and  wh"SrkSh°wl 
connected  at  their  bases  into  a  ring  around  the  stem.  frS 

280 


HORSETAILS.  28 1 

Curious  as  it  may  seem,  these  are  the  leaves  of  the  horsetail. 
The  stem,  if  we  examine  it  farther,  will  be  seen  to  possess  numer- 
ous ridges  which  extend  lengthwise  and  which  alternate  with 
furrows.  Farther,  the  ridges  of  one  node  alternate  with  those 
of  the  internode  both  above  and  below.  Likewise  the  leaves 
of  one  node  alternate  with  those  of  the  nodes  both  above  and 
below. 

573.  Sporangia. — The  end  of  this  fertile  shoot  we  see  pos- 
sesses a  cylindrical  to  conic  enlargement.     This  is  the  fertile 

I  spike,  and  we  note  that  its  surface  is  marked  off 

into  regular  areas  if  the  spores  have  not  yet  been 
disseminated.     If  we  dissect  off  a  few  of  these  por- 
tions of  the  fertile  spike,  and  examine  one  of  them 
with  a  low  magnifying  power,  it  will  appear  like  the 
fig.  322.      We  see  here  that  the  angular  area  is  a 
Fig.  322.      disk-shaped  body,  with  a  stalk  attached  to  its  inner 
phyn  o^equSm  surface,  and  with  several  long  sacs  projecting  from 
Slfg  s^SngfeTn its  inner  face  parallel  with  the  stalk  and  surrounding 
the  same.     These  elongated  sacs  are  the  sporangia, 
and  the  disk  which  bears  them,  together  with  the  stalk  which 
attaches  it  to  the  stem  axis,  is  the  sporophyll,  and  thus  belongs  to 
the  leaf  series.     These  sporophylls  are  borne  in  close  whorls  on 
the  axis. 

574.  Spores. — When  the  spores  are  ripe  the  tissue  of  the 
sporangium  becomes  dry,  and  it  cracks  open  and  the  spores  fall 
out.      If  we   look   at  fig.  323  we  see  that  the  spore  is  covered 
with  a  very  singular  coil  which  lies  close  to  the  wall.     When  the 
spore  dries  this  uncoils  and  thus  rolls  the  spore  about.     Merely 
breathing  upon  these  spores  is  sufficient  to  make  them  perform 
very  curious  evolutions  by  the  twisting  of  these  four  coils  which 
are  attached  to  one  place  of  the  wall.     They  are  formed  by  the 
splitting  up  of  an  outer  wall  of  the  spore. 

575.  Sterile   shoot  of  the  common  horsetail. — When  the 
spores  are   ripe  they  are   soon   scattered,  and  then  the  fertile 
shoot  dies  down.     Soon  afterward,  or  even  while  some  of  the 
fertile  shoots  are  still  in  good  condition,  sterile  shoots  of  the 


282 


MORPHOLOG  Y. 


plant  begin  to  appear  above  the  ground.     One  of  these  is  shown 
in  fig.  325.     This  has  a  much  more  slender  stem  and  is  pro- 


Fig.  323. 

Spore    of  equisetum 
with  elaters  coiled  up. 


Fig.  324- 

Spore  of  equisetum  with  elaters  un- 
coiled. 


vided  with  numerous  branches.  If  we  ex- 
amine the  stem  of  this  shoot,  and  of  the 
branches,  we  see  that  the  same  kind  of 
leaves  are  present  and  that  the  markings  on 
the  stem  are  similar.  Since  the  leaves  of 
the  horsetail  are  membranous  and  not  green, 
the  stem  is  green  in  color,  and  this  per- 
forms the  function  of  photosynthesis.  These 
green  shoots  live  for  a  great  part  of 
the  season,  building  up  material  which  is 
carried  down  into  the  underground  stems, 
where  it  goes  to  supply  the  forming  fertile 
shoots  in  the  fall.  On  digging  up  some  of 
these  plants  we  see  that  the  underground 
sterns  are  often  of  great  extent,  and  that 
both  fertile  and  sterile  shoots  are  attached 
to  one  and  the  same. 

576.   The  scouring  rush,  or  shave  grass. 
— Another  common  species  of  horsetail  in 
the  Northern   States  grows  on  wet    banks, 
or   in  sandy  soil   which  contains    moisture 
along  railroad    embankments.      It    is 
the  scouring  rush  (E.    hyemale),    so 
called  because  it  was  once  used  for 
polishing  purposes.     This  plant  like 
all  the  species  of  the   horsetails  has 


Fig.  325. 

Sterile  plant  of  horsetail  (Equi- 
setum arvensis). 


HORSE  TA ILS.  283 

underground  stems.  But  unlike  the  common  horsetail,  there  is 
but  one  kind  of  aerial  shoot,  which  is  green  in  color  and  fertile. 
The  shoots  range  as  high  as  one  meter  or  more,  and  are  quite 
stout.  The  new  shoots  which  come  up  for  the  year  are  un- 
branched,  and  bear  the  fertile  spike  at  the  apex.  When  the 
spores  are  ripe  the  apex  of  the  shoot  dies,  and  the  next  season 
small  branches  may  form  from  a  number  of  the  nodes. 

577.  Gametophyte  of  equisetum. — The  spores  of  equisetum  have  chloro- 
phyll when  they  are  mature,  and  they  are  capable  of  germinating  as  soon  as 
mature.  The  spores  are  all  of  the  same  kind  as  regards  size,  just  as  we 
found  in  the  case  of  the  ferns.  But  they  develop  prothallia  of  different 
sizes,  according  to  the  amount  of  nutriment  which  they  obtain.  Those 
which  obtain  but  little  nutriment  are  smaller  and  develop  only  antheridia, 
while  those  which  obtain  more  nutriment  become  larger,  more  or  less 
branched,  and  develop  archegonia.  This  character  of  an  independent  pro- 
thallium  (gametophyte)  with  the  characteristic  sexual  organs,  and  the  also 
independent  sporophyte,  with  spores,  shows  the  relationship  of  the  horsetails 
with  the  ferns.  We  thus  see  that  these  characters  of  the  reproductive 
organs,  and  the  phases  and  fruiting  of  the  plant,  are  more  essential  in  deter- 
mining relationships  of  plants  than  the  mere  outward  appearances. 


CHAPTER   XXX. 


CLUB  MOSSES. 

578.  What  are  called  the  "  club  mosses  "  make  up  another 
group  of  interesting  plants  which  rank  as   allies  of  the  ferns. 
They  are  not  of  course  true  mosses,  but  the  general  habit  of 
some  of  the  smaller  species,  and  especially  the 

form  and  size  of  the  leaves,  suggest  a  resem- 
blance to  the  larger  of  the  moss  plants. 

579.  The  clavate  lycopodium. — Here  is  one 
of  the  club  mosses  (fig.  326)  which  has  a  wide 
distribution  and  which  is  well  entitled  to  hold 
the  name  of  club  because  of  the  form  of  the  up- 
right club-shaped  branches.     As  will  be  seen 
from  the  illustration,  it  has  a  prostrate  stem. 
This  stem  runs  for  considerable  distances  on 
the  surface  of  the  ground,  often  partly  buried  in 
the  leaves,  and  sometimes  even  buried  beneath 
the  soil.     The  leaves  are  quite  small,  are  flat- 
tened-awl-shaped,  and  stand  thickly  over  the 
stem,  arranged  in  a  spiral  manner,  which  is  the 
usual   arrangement   of  the  leaves   of  the  club 
mosses.     Here  and  there  are  upright  branches 
which  are  forked  several  times.     The  end  of 
one  or  more  of  these  branches  becomes  pro- 
duced into  a  slender  upright  stem  which  is 
nearly  leafless,   the  leaves  being   reduced  to 
mere  scales.     The  end  of  this  leafless  branch 

then  terminates  in  one  or  several  cylindrical  spore  near  lt- 
heads  which  form  the  club. 

284 


CLUB   MOSSES.  285 

580.  Fruiting  spike  of  Lycopodium  clavatum. — This  club  is 
the  fruiting  spike  or  head  (sometimes  termed  &slrobilus}.  Here 
the  leaves  are  larger  again  and  broader,  but  still  not  so  large  as 
the  leaves  on  the  creeping  shoots,  and  they  are  paler.  If  we  bend 
down  some  of  the  leaves,  or  tear  off  a  few,  we  see  that  in  the 
axil  of  the  leaf,  where  it  joins  the  stem,  there  is  a  somewhat 
rounded,  kidney -shaped  body.  This  is  the  spore-case  or  spo- 
rangium, as  we  can  see  by  an  examination  of  its  contents.  There 
is  but  a  single  spore-case  for  each  of  the  fertile  leaves  (sporophyll). 
When  it  is  mature,  it  opens  by  a  crosswise  slit  as  seen  in  fig.  326. 
When  we  consider  the  number  of  spore -cases  in  one  of  these  club- 
shaped  fruit  bodies  we  see  that  the  number  of  spores  developed 
in  a  large  plant  is  immense.  In  mass  the  spores  make  a  very  fine, 
soft  powder,  which  is  used  for  some 
kinds  of  pyrotechnic  material,  and  for 
various  toilet  purposes. 

581.    Lycopodium   lucidulum. — Another  com- 
mon species  is  figured  at  327.     This  is  Lycopo- 
dium lucidulum.     The  habit  of  the  plant  is  quite 
different.      It  grows  in  damp  ravines,  woods,  and 
moors.     The  older  parts  of  the  stem  are  prostrate, 
while  the  branches  are  more  or  less  ascending. 
It  branches  in  a  forked  manner.     The  leaves  are 
larger  than  in  the    former  species,  and  they  are 
all  of  the  same  size,  there  being  no  appreciable 
difference  between  the  sterile  and 
fertile   ones.    .    The    characteristic 
club  is  not   present    here,  but    the 
spore -cases  occupy  certain  regions  of 
the  stem,  as  shown  at  327.      In  a 
single  season  one  region  of  the  stem 
may  bear  spore-cases,   and  then  a 
sterile  portion  of  the  same  stem  is 

ig- 327.  developed,  which  later  bears  another 
Lycopodium   lucidulum,   bulbils   in    axils    of 

leaves  near  the  top,  sporangia  in  axils  of  leaves  series  of  spore-cases  higher  up. 
below  them.     At  right  is  a  bulbil  enlarged.  .  . 

582.  Bulbils     on     Lycopodium 

lucidulum. — There  is  one  curious  way  in  which  this  club  moss  multiplies. 
One  may  see  frequently  among  the  upper  leaves  small  wedge-shaped  or  heart- 
shaped  green  bodies  but  little  larger  than  the  ordinary  leaves.  These  are  little 


286 


MORPHOLOGY. 


buds  which  contain  rudimentary  shoot  and  root  and  several  thick  green  leaves. 
When  they  fall  to  the  ground  they  grow  into  new  lycopodium  plants,  just  as 
the  bulbils  of  cystopteris  do  which  were  described  in  the  chapter  on  ferns. 

583.  Note. — The  prothallia  of  the  species  of  lycopodium  which  have  been 
studied  are  singular  objects.  In  L.  cernuum  a  cylindrical  body  sunk  in  the 
earth  is  formed,  and  from  the  upper  surface  there  are  green  lobes.  In  L.' 
phlegmaria  and  some  others  slender  branched,  colorless  bodies  are  formed 
which  according  to  Treub  grow  as  a  saphrophyte  in  decayed  bark  of  trees. 
Many  of  the  prothallia  examined  have  a  fungus  growing  in  their  tissue  which 
is  supposed  to  play  some  part  in  the  nutrition  of  the  prothallium. 


The  little  club  mosses  (selaginella). 

584.  Closely  related  to  the  club  mosses  .are  the  selaginellas. 
These  plants  resemble  closely  the  general  habit  of  the  club  mosses, 
but  are  generally  smaller  and  the  leaves  more  delicate.  Some 
species  are  grown  in  conservatories  for  ornament,  the  leaves  of 


Fig.  328.                          Fig.  329.  Fig.  330.  Fig.  331- 

Selaginella      with         Fruiting     spike  Large  spo-  Small  spo- 

three   fruiting    spikes,  showing    large     and  rangium.  rangium. 

(Selaginella  apus.)  small  sporangia. 

such  usually  having  a  beautiful  metallic  lustre.  The  leaves  of  some 
are  arranged  as  in  lycopodium,  but  many  species  have  the  leaves 
in  four  to  six  rows.  Fig.  328  represents  a  part  of  a  selaginella 
plant  (S.  apus).  The  fruiting  spike  possesses  similar  leaves,  but 
they  are  shorter,  and  their  arrangement  gives  to  the  spike  a  four- 
sided  appearance. 


LITTLE   CLUB  MOSSES. 

585.  Sporangia. — On  examining  the  fruiting  spike,  we  find 
as  in  lycopodium  that  there  is  but  a  single  sporangium  in  the 
axil  of  a  fertile  leaf.      But  we  see  that  they  are  of  two  different 
kinds,  small  ones  in  the  axils  of  the  upper  leaves,  and  large  ones 
in  the  axils  of  a  few  of  the  lower  leaves  of  the  spike.     The  micro- 
spores  are  borne  in  the  smaller  spore-cases  and  the  macrospores 
in  the  larger  ones.     Figures   329-331   give  the  details.     There 
are  many  microspores  in  a  single  small  spore-case,  but  3-4  ma- 
crospores in  a  large  spore-case. 

586.  Male  prothallia. — The  prothallia  of  selaginella  are  much 
reduced  structures.     The  microspores  when  mature  are  already 
divided  into  two  cells.     When  they  grow  into  the  mature  pro- 
thallium  a  few  more  cells  are  formed,  and  some  of  the  inner  ones 
form  the  spermatozoids,  as  seen  in  fig.  332.      Here  we  see  that 


Fig.  332. 

Details  of  microspore  and  male  prothallium  of  selaginella ;  ist,  microspore ;  2d,  wall  re- 
moved to  show  small  prothallial  cell  below ;  3d,-  mature  male  prothallium  still  within  the 
wall ;  4th,  small  cell  below  is  the  prothallial  cell,  the  remainder  is  antheridium  with  wall  and 
four  sperm  cells  within  ;  sth  spermatozoid.  After  Beliaieff  and  Pfeffer. 

the  antheridium  itself  is  larger  than  the  prothallia.  Only  an- 
theridia  are  developed  on  the  prothallia  formed  from  the 
microspores,  and  for  this  reason  the  prothallia  are  called  male 
prothallia.  In  fact  a  male  prothallium  of  selaginella  is  nearly 
all  antheridium,  so  reduced  has^the  gametophyte  become  here. 

587.  Female  prothallia. — The  female  prothallia  are  devel- 
oped from  the  macrospores.  The  macrospores  when  mature  have 
a  rough,  thick,  hard  wall.  The  female  prothallium  begins  to 
develop  inside  of  the  macrospore  before  it  leaves  the  sporangium. 
The  protoplasm  is  richer  near  the  wall  of  the  spore  and  at  the 


288 


MORPHOLOG  Y. 


upper  end.  Here  the  nucleus  divides  a  great  many  times,  and 
finally  cell  walls  are  formed,  so  that  a  tissue  of  considerable  ex- 
tent is  formed  inside  the  wall  of  the  spore,  which  is  very 
different  from  what  takes  place  in  the  ferns  we  have 
studied.  As  the  prothallium  matures  the  spore  is  cracked 
at  the  point  where  the  three  angles  meet,  as  shown  in 
fig.  334.  The  archegonia  are  developed  in  this  exposed 
surface,  and  several  can  be  seen  in  the  illustration. 

588.  Embyro. — After  fertilization  the  egg  divides  in  such  a  way 
that  a  long  cell  called  a  suspensor  is  cut  off  from  the  upper  side, 


Fig-  333- 

Section  of  mature  macrospore 
of  selagmella,  showing  female 
prothallium  and  archegonia. 
After  Pfeffer. 


Fig.  334- 

Mature  female  prothallium  of 
selaginella,  just  bursting  open 
the  wall  of  macrospore,  exposing 
archegonia.  After  Pfeffer. 


Fig.  335. 

Seedling  of  sela- 
ginella still  attached 
to  the  macrospore. 
After  Campbell. 


which  elongates  and  pushes  the  developing  embyro  down  into  the  center  of 
the  spore,  or  what  is  now  the  female  prothallium.  Here  it  derives  nourish- 
ment from  the  tissues  of  the  prothallium,  and  eventually  the  root  and  stem 
emerge,  while  a  process  called  the  "  foot  "  is  still  attached  to  the  prothallium. 
When  the  root  takes  hold  on  the  soil  the  embyro  becomes  free. 


CHAPTER  XXXI. 

QUILLWORTS    (ISOETES). 

589.  The  quillworts,  as  they 
are  popularly  called,  are  very 
curious  plants.  They  grow  in 
wet  marshy  places.  They  receive 
their  name  from  the  supposed 
resemblance  of  the  leaf  to  a  quill. 
Fig.  336  represents  one  of  these 
,  quillworts  (Isoetes  engelmannii) . 
The  leaves  are  the  prominent 
part  of  the  plant,  and  they  are 
about  all  that  can  be  seen  except 
the  roots,  without  removing  the 
leaves.  Each  leaf,  it  will  be 
seen,  is  long  and  needle-like,  ex- 
cept the  basal  part,  which  is 
expanded,  not  very  unlike,  in  out- 
line, a  scale  of  an  onion.  These 
expanded  basal  portions  of  the 
leaves  closely  overlap  each  other, 
and  the  very  short  stem  is  com- 
pletely covered  at  all  times.  Fig. 
338  is  from  a  longitudinal  sec- 
tion of  a  quillwort.  It  shows 
the  form  of  the  leaves  from  this 
Fig. 336.  view  (side  view),  and  also  the 

Isoetes,  mature  plant,  sporophyte  stage,   general  outline  of  the  short  stem, 

which  is  triangular.     The  stem  is  therefore  a  very  short  object. 

289 


290 


MORPHOLOGY. 


590.  Sporangia  of  isoetes. — If  we  pull  off  some  of  the 
leaves  of  the  plant  we  see  that  they  are  somewhat  spoon-shaped 
as  in  fig.  337.  In  the  inner  surface  of  the  expanded  base  we 
note  a  circular  depression  which  seems  to  be  of  a  different  text- 


-  337. 

Base  of  leaf  of  isoetes, 
showing  sporangium  with 
macrospores.  (Isoetes  en- 
gelmannii.) 


Fig.  338. 

Section  of  plant  of  Isoetes  engelmahii,  showing  cup- 
shaped  stem,  and  longitudinal  sections  of  the  sporan- 
gia in  the  thickened  bases  of  the  leaves^ 


ure  from  the  other  portions  of  the  leaf.  This  is  a  sporangium. 
Beside  the  spores  on  the  inside  of  the  sporangium,  there  are 
strands  of  sterile  tissue  which  extend  across  the  cavity.  This  is 
peculiar  to  isoetes  of  all  the  members  of  the  class  of  plants  to 
which  the  ferns  belong,  but  it  will  be  remembered  that  sterile 
strands  of  tissue  are  found  in  some  of  the  liverworts  in  the  form 
of  elaters. 

591.  The  spores  of  isoetes  are  of  two  kinds,  small  ones 
(microspores)  and  large  ones  (macrospores),  so  that  in  this 
respect  it  agrees  with  selaginella,  though  it  is  so  very  different  in 
other  respects.  When  one  kind  of  spore  is  borne  in  a  sporan- 


QUILLWORTS.  2gi 

gium  usually  all  in  that  sporangium  are  of  the  same  kind,  so  that 
certain  sporangia  bear  microspores,  and  others  bear  macrospores. 
But  it  is  not  uncommon  to  find  both  kinds  in  the  same  sporan- 
gium. When  a  sporangium  bears  only  microspores  the  number 
is  much  greater  than  when  one  bears  only  macrospores. 

592.  If  we  examine  some  of  the  microspores  of  isoetes  we  see  that  they  are 
shaped  like  the  quarters  of  an  apple,  that  is  they  are  of  the  bilateral  type  as 
seen  in  some  of  the  ferns  (asplenium). 

593.  Male  prothallia. — In  isoetes,  as  in  selaginella,  the  microspores  de- 
velop only  male  prothallia,  and  these  are  very  rudimentary,  one  division  of 
the  spore  having  taken  place  before  the  spore  is  mature,  just  as  in  selagi- 
nella. 

594.  Female  prothallia. — These  are  developed  from  the  macrospores.  The 
latter  are  of  the  tetrahedral  type.     The  development  of  the  female  prothal- 
lium  takes  place  in  much  the  same  way  as  in  selaginella,  the  entire  prothal- 
lium  being  enclosed  in  the  macrospore,  though  the  cell  divisions  take  place 
after  it  has  left  the  sporangium.     When  the  archegonia  begin  to  develop 
the  macrospore  cracks  at  the  three  angles  and  the  surface  bearing  the  arche- 
gonia projects  slightly  as  in  selaginella.      Absorbing  organs   in  the  form  of 
rhizoids  are  very  rarely  formed. 

595.  Embryo. — The   embryo  lies  well   immersed  in  the  tissue  of  the  pro- 
thallium,  though  there  is  no  suspensor  developed  as  in  selaginella. 


CHAPTER    XXXII. 

COMPARISON  OF  FERNS  AND  THEIR  RELATIVES. 

596.  Comparison  of  selaginella  and  isoetes  with  the  ferns. — On  compar- 
ing selaginella  and  isoetes  with  the  ferns,  we  see  that  the  sporophyte  is,  as 
in  the  ferns,  the  prominent  part  of  the  plant.     It  possesses  root,  stem,  and 
leaves.     While  these  plants  are  not  so  large  in  size  as  some  of  the  ferns, 
still  we  see  that  there  has  been  a  great  advance  in  the  sporophyte  of  selagi- 
nella and  isoetes  upon  what  exists  in  the  ferns.     There  is  a  division  of  labor 
between  the  sporophylls,  in  which  some  of  them  bear  microsporangia  with 
microspores,  and  some,  bear  macrosporangia  with  only  macrospores.     In  the 
ferns  and  horsetails  there  is  only  one  kind  of  sporophyll,  sporangium,  and 
spore  in  a  species.     By  this  division  of  labor,  or  differentiation,  between  the 
sporophylls,  one  kind  of  spore,  the  microspore,  is  compelled  to  form  a  male 
prothallium,  while  the  other  kind  of  spore,  the  macrospore,  is  compelled  to 
form  a  female  prothallium.     This  represents  a  progression  of  the  sporophyte 
of  a  very  important  nature. 

597.  On  comparing  the  gametophyte  of  selaginella  and  isoetes  with  that 
of  the  ferns,  we  see  that  there  has  been  a  still  farther  retrogression  in  size 
from  that  which  we  found  in  the  independent  and  large  gametophyte  of  the 
liverworts  and  mosses.      In  the  ferns,  while  it  is  reduced,   it  still  forms 
rhizoids,  and  leads  an  independent  life,  absorbing  its  own  nutrient  materials, 
and  assimilating  carbon.     In  selaginella  and  isoetes  the  gametophyte  does 
not  escape  from  the  spore,  nor  does  it  form  absorbing  organs,  nor  develop 
assimilative  tissue.     The  reduced  prothallium  develops  at  the  expense  of 
food  stored  by  the  sporophyte  while  the  spore  is  developing.     Thus,  while 
the  gametophyte  is  separate  from  the  sporophyte  in  selaginella  and  isoetes, 
it  is  really  dependent  on  it  for  support  or  nourishment. 

598.  The  important  general  characters  possessed  by  the  ferns  and  their 
so-called  allies,  as  we  have  found,  are  as  follows:  The  spore-bearing  part, 
which  is  the  fern  plant,  leads  an  independent  existence  from  the  prothallium. 
and  forms  root,  stem,  and  leaves.  The  spores  are  borne  in  sporangia  on 
the  leaves.  The  prothallium  also  leads  an  independent  existence,  though  in 
isoetes  and  selaginella  it  has  become  almost  entirely  dependent  on  the  sporo- 

292 


FEKNS:    CLASSIFICATION.  295 

Classification  of  the  Pteridophytes. 

Of  the  living  pteridophytes  four  classes  may  be  recognized. 
CLASS   FILICINEJE.* 

This  class  includes  the  ferns.     Four  orders  may  be  recognized. 

600.  Order  Ophioglossales.     (One  Family,  Ophioglossacese). — This  order 
includes   the   grapeferns    (Botrychium),    so  called   because   of    the    large 
botryoid  cluster  of  sporangia,  resembling  roughly  a  cluster  of  grapes;    and 
the  adder-tongue  (Ophioglossum),  the  sporangia  being  embedded  in  a  long 
tongue-like  outgrowth  from  the  green  leaf.     Botrychium  and   Ophioglos- 
sum are  widely  distributed.     The  roots  are  fleshy,  nearly  destitute  of  root 
hairs,  and  contain  an  endophytic  fungus,  so  that  the  roots  are  mycorhiza. 
The  gametophyte  is  subterranean,  and  devoid  of  chlorophyll.     In  Botry- 
chium virginianum,  an  endophytic  fungus  has  been  found  in  the  prothal- 
lium.     Another  genus  (Helminthostachys)  with  one  species  is  limited  to 
the  East  Indies. 

601.  Order  Marattiales  (One  Family,  Marattiaceae). — These  are  trop- 
ical ferns,  with  only  four  or  five   living   genera  (Marattia,  Danaea,  etc.). 
They  resemble  the  typical  ferns,  but  the  sporangia  are  usually  united,  sev- 
eral forming  a  compound  sporangium,  or  synangium.  ^ 

The  Ophioglossales  and  Marattiales  are  known  as  eusporangiate  ferns, 
while  the  following  order  includes  the  leptosporangiate  ferns. 

602.  Order  Filicales.— This  order    includes    the  typical    ferns.     Eight 
families  are  recognized. 

Family  Osmundacece. — Three  genera  are  known  in  this  family.  Os- 
munda  has  a  number  of  species,  three  of  which  are  found  in  the  Eastern 
United  States;  the  cinnamon-fern  (O.  cinnamomea),  the  royal  fern  (O. 
regalis),  and  Clayton's  fern  (O.  claytoniana).  No  species  of  this  family 
are  found  on  the  Pacific  coast. 

Family  Gleicheniacea. — These  ferns  are  found  chiefly  in  the  tropics,  and 
in  the  mountain  regions  of  the  temperate  zones  of  South  America.  There 
are  two  genera,  Gleichenia  containing  all  but  one  of  the  known  species. 

Family  Matoniacece.—  One  genus,  Matonia,  in  the  Malayan  region. 

Family  Schizceacea. — These  are  chiefly  tropical,  but  two  species  are 
found  in  eastern  North  America,  Schizaea  pusilla  and  Lygodium  palma- 
tum,  the  latter  a  climbing  fern. 

Family  Hymenophyllacea. — These  are  known  as  the  filmy  ferns  because 
of  their  thin,  delicate  leaves.  They  grow  only  in  damp  or  wet  regions, 
mostly  in  the  tropics,  but  a  few  species  occur  in  the  southern  United  States. 

Family  Cyatheacece. — These  are  known  as  the  tree-ferns,  because  of  the 


*  As  class  Filicales  in  Engler  and  Prantl. 


296  MORPHOLOG  y. 

large  size  which  many  of  them  attain.  They  occur  chiefly  in  tropical  moun- 
tainous regions,  many  of  them  palm-like  and  imposing  because  of  the  large 
trunks  and  leaves.  Dicksonia,  Cyathea,  Cibotium,  Alsophila,  are  some  of 
the  most  conspicuous  genera. 

Family  Parker iacece. — There  is  a  single  species  in  this  family  (Cera- 
topteris  thalictroides),  abundant  in  the  tropics  and  extending  into  Florida. 
It  is  aquatic. 

Family  Polypodiacece. — This  family  includes  the  larger  number  of  living 
ferns  and  many  genera  and  species  are  found  in  North  America.  Exam- 
ples, Polypodium,  Pteridium  (=Pteris),  Adiantum,  etc. 

603.  Order  Hydropterales  (or  Salviniales). — The  members  of  this  order 
are  peculiar,  aquatic  ferns,  some  floating  on  the  water  (Azolla,  Salvinia), 
while  others  are  anchored  to  the  soil  by  roots  (Marsilia,  Pilularia).     They 
are  known  as  water  ferns.     The  sporangia  are  of  two  kinds,  one  containing 
large  spores  (macrospores)  and  the  other  small  spores  (microspores).     They 
are  therefore  heterosporous  ferns. 

Family  Salmniacea. — There  are  two  genera,  Salvinia  and  Azolla. 
Family  Marsiliacea. — Two  genera,  Marsilia  and  Pilularia.     In  this  family 
the  sporangia  are  enclosed  in  a  sporocarp,  which  forms  a  pod-like  structure. 
CLASS   EQUISETINE2E.* 

604.  Order    Equisetales. — The  single  order   contains   a   single   family, 
Equisetaceae,  among  the  living  forms,  and  but  a  single  genus,  Equisetum. 
There  are  about  twenty-four  species,  with  fourteen  in  the  United  States  (see 

Chapter  XXIX). 

CLASS   LYCOPODILNEJE.f 

605.  Order   Lycopodiales. — The  first  two  families  of  this  order  include 
the  homosporous  Lycopodiineae,  while  the  Selaginellaceae  are  heterosporous. 

Family  Lycopodiacea. — There  are  two  genera.  Lycopodium  (club 
moss)  includes  many  species,  most  of  them  tropical,  but  a  number  in  tem- 
perate and  subarctic  regions.  The  gametophyte  of  many  species  is  tuber- 
ous, lacks  chlorophyll,  and  in  some  there  lives  an  endophytic  fungus.  Phyl- 
loglossum  with  one  species  is  found  in  Australia. 

Family  Psilotacece. — There  are  two  genera.  Psilotum  chiefly  in  the 
tropics  has  one  species  (P.  triquetrum)  in  the  region  of  Florida. 

Family  Selaginellacece. — These  include  the  little  club  mosses,  with  one 
genus,  Selaginella  (see  Chapter  XXX). 

CLASS   ISOETINEJE. 

606.  Order  Isoetales,  with  one  family  Isoetaceae  and  one  genus  Isoetes 
(see  Chapter  XXXI).     There  are  about  fifty  species,  with  about  sixteen  in 
the  United  States. 


*  As  class  Equisetales  in  Engler  and  Prantl. 
f  As  class  Lycopodiales  in  Engler  and  Prantl. 


CHAPTER   XXXIII. 

GYM  NOSPERMS. 
The   white   pine. 

607.  General  aspect  of  the  white  pine. — The  white  pine 
(Pinus  strobus)  is  found  in  the  Eastern  United  States.  In 
favorable  situations  in  the  forest  it  reaches  a  height  of  about  50 
meters  (about  160  feet),  and  the  trunk  a  diameter  of  over  i 
meter.  In  well-formed  trees  the  trunk  is  straight  and  towering; 
the  branches  where  the  sunlight  has  access  and  the  trees  are  not 
crowded,  or  are  young,  reaching  out  in  graceful  arms,  form  a 
pyramidal  outline  to  the  tree.  In  old  and  dense  forests  the  lower 
branches,  because  of  lack  of  sunlight,  have  died  away,  leaving 
tall,  bare  trunks  for  a  considerable  height. 

608.  The  long  shoots  of  the  pine. — The  branches  are  of  two  kinds.     Those 
which  we  readily  recognize  are  the  long  branches,  so  called  because  the 
growth  in  length  each  year  is  considerable.     The  terminal  bud  of  the  long 
branches,  as  well  as  of  the  main  stem,  continues  each  year  the  growth  of  the 
main  branch  or  shoot;  while  the  lateral  long  branches  arise  each  year  from 
buds  which  are  crowded  close  together  around  the  base  of  the  terminal  bud. 
The  lateral  long  branches  of  each  year  thus  appear  to  be  in  a  whorl.     The 
distance  between  each  false  whorl  of  branches,  then,  represents  one  year's 
growth  in  length  of  the  main  stem  or  long  branch. 

609.  The  dwarf  shoots  of  the  pine. — The  dwarf  branches  are  all  lateral 
on  the  long  branches,  or  shoots.     They  are  scattered  over  the  year's  growth, 
and  each  bears  a  cluster  of  five  long,  needle-shaped,  green  leaves,  which 
remain  on  the  tree  for  several  years.     At  the  base  of  the  green  leaves  are 
a  number   of  chaff-like  scales,   the  previous  bud  scales.     While  the  dwarf 
branches  thus  bear  green  leaves,  and  scales,  the  long  branches  bear  only 
thin  scale-like  leaves  which  are  not  green. 

297 


298 


MORPHOLOGY. 


610.  Spore-bearing  leaves  of  the  pine. — The  two  kinds  of 
spore-bearing  leaves  of  the  pine,  and  their  close  relatives,  are 
so  different  from  anything  which   we  have  yet  studied,  and  are 
so  unlike  the   green  leaves  of  the  pine,  that  we  would  scarcely 
recognize  them  as  belonging  to  this  category.      Indeed  there  is 
great  uncertainty  regarding  their  origin. 

611.  Male  cones,  or  male  flowers. — The  male  cones  are  borne 
in  clusters  as  shown  in  fig.  339.      Each  compact,  nearly  cylindri- 


Fig-  339- 
Spray  of  white  pine  showing  cluster  of  male  cones  just  before  the  scattering  of  the  pollen. 

cal,  or  conical  mass  is  termed  a  cone,  or  flower,  and  each  arises 
in  place  of  a  long  lateral  branch.     One  of  these  cones  is  shown 


GYMNOSPERMS:    WHITE  PINE. 


299 


considerably  enlarged  in  fig.  340.  The  central  axis  of  each 
cone  is  a  lateral  branch,  and  belongs  to  the  stem  series.  The 
stem  axis  of  the  cone  can  be  seen  in  fig.  341.  It  is  completely 
covered  by  stout,  thick,  scale-like  outgrowths.  These  scales 
are  obovate  in  outline,  and  at  the  inner  angle  of  the  upper  end 


Fig.  34°.  Fig-  34i.  Fig.  342. 

Staminate  cone  of  white '        Section     of    staminate        Two     sporo- 
pine,  with  bud  scales  re-    cone,  showing  sporangia,     phylls  removed,    *    ,'  « 
moved  on  one  side.  showing     open-        J^ 

ing  of  sporangia. 

there  are  several  rough,  short  spines.  They  are  attached  foy 
their  inner  lower  angle,  which  forms  a  short  stalk  or  petiote, 
and  continues  through  the  inner  .face  of  the  scale  as  a  < '  mid- 
rib." What  corresponds  to  the  lamina  of  the  scale-like,  leaf 
bulges  out  on  each  side  below  and  makes  the  bulk  of  the  scale. 
These  prominences  on  the  under  side  are  the  sporangia  (micro- 
sporangia).  There  are  thus  two  sporangia  on  a,  sporophyll 
(microsporophyll).  When  the  spores  (microspores),  which 
here  are  usually  called  pollen  grains,  are  mature  each  sporangium, 

or   anther   locule,  splits   down   the    middle   as 

shown  in  fig.  342,  and  the  spores  are  set  free. 
612.    Microspores   of   the   pine,    or    pollen 

grains. — A  mature  pollen  grain  of  the  pine  is 
Pollen0  "grain    of  shown  in  fig.  343.      It  is  a  queer-looking  object, 

possessing  on  two  sides  an  air  sac,  formed  by  the 
upheaval  of  the  outer  coat  of  the  spore  at  these  two  points. 


Fig.  343- 


3oo 


MORPHOLOGY. 


When  the  pollen  is  mature,  the  moisture  dries  out  of  the  scale 
(or  stamen,  as  it  is  often  called  here)  while 
it  ripens.      When  a   limb,  bearing  a  cluster 
of  male  cones,  is  jarred  by  the  hand,  or  by 
currents  of  air,  the  split  suddenly  opens,  and 
a  cloud  of  pollen  bursts  out  from  the  numer- 
ous anther  locules.      The   pollen  is 
thus  borne  on  the  wind  and  some  of 

it   falls    on   the 

female  flowers. 


Fig.  344- 

White  pine,  branch  with  cluster  of 
mature  cones  shedding  the  seed.  A 
few  young  cones  four  months  old 
are  shown  on  branch  at  the  left. 
Drawn  from  photograph. 

613.  Form  of  the  ma- 
ture female  cone. — A 

cluster  of  the  white- 
pine  cones  is  shown  in 
fig.  344.  These  are 
mature,  and  the  scales 
have  spread  as  they  do  when  mature  and  becoming  dry,  in 

order  that  the  seeds  may  be  set  at  liberty.     The  general  out- 

,.*• 


Fig.  345. 

Mature  cone  of  white  pine 
at  time  of  scattering  of  the 
seed,  nearly  natural  size. 


GYMNOSPERMS:    WHITE  PINE.  3OI 

line   of  the  cone   is  lanceolate,   or  long  oval,  and   somewhat 
curved.     It  measures  about  io-i$cm  long.     If  we  remove  one 


Pig.  346.  Fig.  347-  Fig-  348.  Fig.  349.  Fig.  35°. 

Sterile  scale.  Scale  with  Seeds  have  Back  of  scale  Winged 
Seeds  undevel-  well -developed  split  off  from  with  small  cover  seed  free  from 
oped.  seeds.  scale.  scale.  scale. 

Figs.  346-350.— White  pine  showing  details  of  mature  scales  and  seed. 

of  the  scales,  just  as  they  are  beginning  to  spread,  or  before  the 
seeds  have  scattered,  we  shall  find  the  seeds  at- 
tached to  the  upper  surface  at  the  lower  end. 
There  are  two  seeds  on  each  scale,  one  at  each 
lower  angle.  They  are  ovate  in  outline,  and 
shaped  somewhat  like  a  biconvex  lens.  At  this 
time  the  seeds  easily  fall  away,  and  may  be 
freed  by  jarring  the  cone.  As  the  seed  is 
detached  from  the  scale  a  strip  of  tissue  ,from 
the  latter  is  peeled  off.  This  forms  a  "  wing  " 
for  the  seed.  It  is  attached  to  one  end  and  is 
shaped  something  like  a  knife  blade.  On  the 
back  of  the  scale  is  a  small  appendage  known 
as  the  cover  scale. 

614.  Formation  of  the  female  pine  cone. — The  female 
flowers  begin  their  development  rather  late  in  the  spring 
of  the  year.  They  are  formed  from  terminal  buds  of 
the  higher  branches  of  the  tree.  In  this  way  the  cone 
may  terminate  the  main  shoot  of  a  branch,  or  of  the 
Fig.  351.  lateral  shoots  in  a  whorl.  After  growth  has  proceeded 

Female  cones  of  the  for  some  time  in  the  spring,  the  terminal  portion  begins 
pine  at  time  of  pollina- 
tion, about  natural  size,  to  assume  the  appearance  of  a  young  female  cone  or 


302 


MORPHOLOG  Y. 


flower.  These  young  female  cones,  at  about  the  time  that  the  pollen  is 
escaping  from  the  anthers,  are  long  ovate,  measuring  about  6-iomm  long. 
They  stand  upright  as  shown  in  fig.  351. 

615.  Form  of  a  "  scale  "  of  the  female  flower. — If  we  remove 
one  of  the  scales  from  the  cone  at  this  stage  we  can  better  study 
it  in  detail.  It  is  flattened,  and  oval  in 
outline,  with  a  stout  "  rib,"  if  it  may  be  so 
called,  running  through  the  middle  line  and 
terminating  in  a  point.  The  scale  is  in 
two  parts  as  shown  in  fig.  3,54,  which  is  a 
view  of  the  under  side.  The  small  "  out- 
growth ' '  which  appears  as  an  appendage  is 
the  cover  scale,  for  while  it  is  smaller  in  the 
pine  than  the  other  portion,  in  some  of 
the  relatives  of  the  pine  it  is  larger  than  its 
mate,  and  being  on  the  outside,  covers  it. 
(The  inner  scale  is  sometimes  called  the  ovu- 
liferous  scale,  because  it  bears  the  ovules. ) 

616.   Ovules,  or  macrosporangia,  of  the 
pine. — At  each  of  the  lower  angles  of  the 


Fig.  352. 

Section  of  female  cone 
of  white  pine,  showing 
young  ovules  (macrospo- 
rangia) at  base  of  the  ovu- 
liferous  scales. 


Fig.  353. 

Scale  of  white  pine  with  the 
two  ovules  at  base  of  ovulif- 
erous  scale. 


Fig.  354- 

Scale  of  white  pine  seen 
from  the  outside,  showing  the 
cover  scale. 


scale  is  a  curious  oval  body  with  two  curved,  forceps-like  pro- 
cesses at  the  lower  and  smaller  end.  These  are  the  macro- 
sporangia,  or,  as  they  are  called  in  the  higher  plants,  the  ovules. 
These  ovules,  as  we  see,  are  in  the  positions  of  the  seeds  on  the 


GYMNOSPERMS:    WHITE   PINE. 


303 


mature  cones.     In  fact  the  wall  of  the  ovule  forms  the  outer  coat 
of  the  seed,  as  we  will  later  see. 

617.  Pollination. — At  the  time  when  the  pollen  is  mature  the 
female  cones  are  still  erect  on  the  branches,  and  the  scales,  which 
during  the  earlier  stages  of  growth  were  closely  pressed  against 
one  another  around  the  axis,  are  now 
spread  apart.  As  the  clouds  of  pollen 
burst  from  the  clusters  of  the  male  cones, 
some  of  it  is  wafted  by  the  wind  to  the 
female  cones.  It  is  here  caught  in  the 
open  scales,  and  rolls  down  to  their  bases, 
where  some  of  it  falls  between  these 
forceps-like  processes  at  the 
lower  end  of  the  ovule.  At 


Branch  of  white  pine  showing  young  female  cones  at  time  of  pollination  on  the  ends  of 
"  '    '  -     -          "      -fizal 


Fig.  355- 
remale  cor 
ihe  branches,  and  one-year-old  cones  below,  near  the  time  of  fertilization. 

this  time  the  ovule  has  exuded  a  drop  of  a  sticky  fluid  in  this 
depression  between  the  curved  processes  at  its  lower  end.  The 
pollen  sticks  to  this,  and  later,  as  this  viscid  substance  dries  up, 
it  pulls  the  pollen  close  up  in  the  depression  against  the  lower 


394 


MORPHOLOG  Y. 


end  of  the  ovule.     This  depression  is  thus  known  as  the  pollen 

chamber. 

618.  Now  the  open  scales  on  the  young  female  cone  close  up 

again  so  tightly  that  water  from  rains  is  excluded.  What  is  also 
very  curious,  the  cones,  which  up  to  this 
time  have  been  standing  erect,  so  that 
the  open  scale  could  catch  the  pollen, 
now  turn  so  that  they  hang  downward. 
This  more  certainly  excludes  the  rains, 
since  the  overlapping  of  the  scales  forms 
a  shingled  surface.  Quantities  of  resin 
are  also  formed  in  the  scales,  which 
exudes  and  makes  the  cone  practically 
impervious  to  water. 

619.  The  female  cone  now  slowly 
grows  during  the  summer  and  autumn, 
increasing  but  little  in  size  during  this 
time.  During  the  winter  it  rests,  that 
is,  ceases  to  grow.  With  the  coming  of 


Fig.  356. 

Macrospprangium   of    pine 
(ovule),     int,  integument;  n, 


Songy  Ssue^Sre'r  Fei  spring,   growth   commences    again    and 
at  an  accelerated  rate.     The  increase  in 

size  is  more  rapid.  The  cone  reaches  maturity  in  September. 
We  thus  see  that  nearly  eighteen  months  elapse  from  the  begin- 
ning of  the  female  flower  to  the  maturity  of  the  cone,  and  about 
fifteen  months  from  the  time  that  pollination  takes  place. 

620.  Female  prothallium  of  the  pine. — To  study  this  we  must  make  care- 
ful longitudinal  sections  through  the  ovule  (better  made  with  the  aid  of  a 
microtome).  Such  a  section  is  shown  in  fig.  358.  The  outer  layer  of  tis- 
sue, which  at  the  upper  end  (point  where  the  scale  is  attached  to  the  axis  of 
the  cone)  stands  free,  is  the  ovular  coat,  or  integument.  Within  this  integu- 
ment, near  the  upper  end,  there  is  a  cone-shaped  mass  of  tissue.  This 
mass  of  tissue  is  the  nucellus,  or  the  macro  sporangium  proper.  In  the 
lower  part  of  the  nucellus  in  fig.  356  can  be  seen  a  rounded  mass  of  "spongy 
tissue  "  (spt),  which  is  a  special  nourishing  tissue  of  the  nucellus,  or  spo- 
rangium, around  the  macrospore.  Within  this  can  be  seen  an  axile  row 
of  three  cells  (an :  m).  The  lowest  one,  which  is  larger  than  the  other 
two,  is  the  macrospore.  Sometimes  there  are  four  of  these  cells  in  the  axile 
row.  This  axile  row  of  three  or  four  cells  is  formed  by  the  two  successive 


GYMNOSPERMS:    WHITE  PINE. 


305 


6. 


Fig.  357- 

Pollen  grains  of  pine.     One  of  them  germinat- 
p1  and  p2,  the  two  disintegrated  prothallial 


divisions  of  a  mother  cell  in  the  nucellus.     So  it  would  appear  that  these 

three   or    four   cells    are   all 

spores. 

Only  one  of  them,  however, 
the  lower  one,  develops;  the 
others  are  disorganized  and 
disappear.  The  nucleus  of 
the  macrospore  now  divides 
several  times  to  form  several 
free  nuclei  in  the  now  enlarg- 
ing cavity,  much  as  the  nu- 
cleus of  the  macrospore  in 
Selaginella  and  Isoetes  divides 

within  the  spore.  The  de-  cells,  =  sterile'  part  of  male  gametophyte;  a.c.t 
velopment  thus  far  takes  place  cfe^s^  r° tUb°f  ant1heridium '•  »•«-,  vegetative  nu- 
during  the  first  summer,  and  antheridium;  s.g.,  starch  grains.  (After  Ferguson.) 
now  with  the  approach  of  winter  the  very  young  female  prothallium  goes 

into  rest  about  the  stage  shown  in 
fig-  35^.  The  conical  portion  of 
the  nucellus  which  lies  above  is  the 
nucellar  cap. 

621.  Male  prothallia.— By  the 
time  the  pollen  is  mature  the  male 
prothallium  is  already  partly 
formed.  In  fig.  343  we  can  see 
two  well-formed  cells.  Two  other 
cells  are  formed  earlier,  but  they 
become  so  flattened  that  it  is  diffi- 
cult to  make  them  out  when  the 
pollen  grain  is  mature.  These  are 
shown  in  fig.  357,  p1  and  p2,  and 
they  are  the  only  sterile  cells  of  the 
male  prothallium  in  the  pines.  The 
large  cell  is  the  antheridium  wall, 
its  nucleus  v.n.  in  fig.  357.  The 
smaller  cell,  a.c.,  is  the  central  cell 
of  the  antheridium.  During  the 
summer  and  autumn  the  male 
prothallium  makes  some  farther 
growth,  but  this  is  slow.  The 
Fig.  358.  larger  cell,  called  the  vegetative 

Section  of  ovule  of  white  pine,    int,  in-  cell  or  tube  cell,  which  is  in  reality 
tegument;    pc,  pollen  chamber;    pt,  pollen  . 

tube:  n,  nucleus;  m,  macrospore  cavity.        the  wall  of  the  antheridium,  elon- 


306 


MORPHOLOG  Y. 


gates  by  the  formation  of  a  tube,  forming  a  sac,  known  as  the  pollen  tube 
It  is  either  simple  or  branched.  It  grows  down  into  the  tissue  of  the  nu- 
cellus,  and  at  a  stage  represented  in  fig.  358,  winter  overtakes  it  and  it 
rests.  At  this  time  the  central  cell  has  divided  into  two  cells,  and  the 
vegetative  nucleus  is  in  the  pollen  tube. 

622.  The  endosperm. — In  the  following  spring  growth  of  all  these  parts 


Fig.  359- 

Section  of  nucellus  and  endosperm  of  white  pine.  The  inner  layer  of  cells  of 
the  integument  shown  just  outside  of  nucellus;  arch,  archegonium;  en,  egg  nu- 
cleus. In  the  nucellar  cap  are  shown  three  pollen  tubes,  vn,  vegetative  nucleus 
or  tube  nucleus;  stc,  stalk  cell;  spn,  sperm  nuclei,  the  larger  one  in  advance  is 
the  one  which  unites  with  the  egg  nucleus.  The  archegonia  are  in  the  endosperm 
or  female  gametophyte.  (After  Ferguson.) 

continues.     The  nuclei  in  the  macrospore  divide  to  form  more,  and  event- 
ually cell  walls  are  formed  between  them  making  a  distinct  tissue,  known 


GYMNOSPERMS;    WHITE  PINE. 


307 


as  the  endosperm.     This  endosperm  continues  to  grow  until  a  large  part  of 
the  nucellus  is  consumed  for  food. 

623.  Female  prothallium  and  archegonia. — The  endosperm  is  the  female 
pro  thallium.     This  is  very  evident  from  the  fact  that  severa*  archegonia 
are  developed  in  it  usually  on  the  side  toward  the  pollen  chamber.     The 
archegonia  are  sexual  organs,  and  since  the  sexual  organs  are  developed  on 
the  gametophyte,  therefore,  the  endosperm  is  the  female  gametophyte,  or 
prothallium.     In  fig.  359  are  represented  two  archegonia  in  the  endosperm 
and  the  pollen  tubes  are  growing  down  through  the  nucellus.     The  arche- 
gonia are  quite  large,  the  wall  is  a  sheath  or  jacket  of  cells  which  encloses 
the  very  large  egg  which  has  a  large  nucleus  in  the  center. 

624.  Pollen  tube  and  sperm  cells. — While  the  endosperm  (female  pro- 
thallium)    and   archegonia   are   developing   the   pollen   tube   continues   its 
growth  down  through  the  nucellar  cap,  as  shown  in  fig.  359.     At  the  same 
time  the  two    cells  which  were  formed  in 

the  pollen  grain  (antheridium)  from  the 
central  cell  move  down  into  the  tube.  One 
of  these  is  the  "generative"  cell,  or  "body" 
cell,  and  the  other  is  called  the  stalk  cell, 
though  it  is  more  properly  a  sterile  half  of 
the  central  cell.  The  nucleus  of  the  gener- 
ative cell,  about  the  time  the  archegonium 
is  mature,  divides  to  form  two  nuclei, 
which  are  the  sperm  nuclei,  and  the  one 
in  advance  is  the  larger,  though  it  is  much 
smaller  than  the  egg  nucleus. 

625.  Fertilization.— Very  soon  after  the 
archegonia  are  mature  (early  in  June  in  the 
northern    United    States)   the    pollen  tube 
grows  through  into  the   archegonium  and 
empties  the  two  sperm  nuclei,  the  vegetative 
nucleus  and  the  stalk  cell,  into  the  proto- 
plasm of  the  large  egg.     The  larger  of  the 
two  sperm  nuclei  at  once  comes  in  contact 
with  the  very  large  egg  nucleus  and  sinks 
down  into  a  depression   of  the   same,  as 
shown  in  fig.  361.     These  two  nuclei,  in  the 
pines,  do  not  fuse  into  a  resting  nucleus,  but 

at  once  organize  the  nuclear  figure  for  the  whit?  pinf  cuttine  °ff  thieTventral 
-     .    j.   .  .  canal    cell    at    the    apex    of    the 

nrst  division  of  the   embrvo.      Two    nuclei  archegonium.       End,  endosperm; 


Fig.  360. 
Last  division  of  the  egg  in  the 


are  thus  formed,  and  these  divide  to  form 


Arch,  archegonium. 


four  nuclei  which  sink  to  the  bottom  of  the  archegonium  and  there  organ- 


308 


MORPHOLOGY. 


ize  the  embryo  which  pushes  its  way  into  the  endosperm  from  which  it 
derives  its  food  (fig.  362). 

626.  Homology  of  the  parts  of  the  female  cone. — Opinions  are  divided  as 
to  the  homology  of  the  parts  of  the  female  cone  of  the  pine.  Some  consider 
the  entire  cone  to  be  homologous  with  a  flower  of  the  angiosperms.  The 


Fig.  361- 

Archegonium  of  white  pine  at  stage  of  fertilization,  en,  egg  nucleus;  spn,  sperm 
nucleus  in  conjugation  with  it;  no,  nutritive  bodies  in  cytoplasm  of  large  egg; 
cpt,  cavity  of  pollen  tube;  vn,  vegetative  nucleus  or  tube  nucleus;  sc,  stalk  cell; 
spn,  second  sperm  nucleus:  pr,  portion  of  prothallium  or  endosperm;  sg,  starch 
grains  in  pollen  tube.  The  sheath  of  jacket  cells  of  the  archegonium  is  not  shown. 
(After  Ferguson.) 

entire  scale  according  to  this  view  is  a  carpel,  or  sporophyll,  which  is  divided 
into  the  cover  scale  and  the  ovuliferous  scale.  This  division  of  the  sporo- 
phyll is  considered  similar  to  that  which  we  have  in  isoetes,  where  the  spo- 
rophyll has  a  ligule  above  the  sporangium,  or  as  in  ophioglossum,  where  the 
leaf  is  divided  into  a  fertile  and  a  sterile  portion. 

Others  believe  that  the  ovuliferous  scale  is  composed  of  two  leaves  situ- 
ated laterally  and  consolidated  representing  a  shoot  in  the  axis  of  the  bract. 
There  is  some  support  for  this  in  the  fact  that  in  certain  abnormal  cones 
which  show  proliferation  a  short  axis  appears  in  the  axil  of  the  bract  and 


GYMNOSPERMS:    WHITE  PINE. 


309 


bears  lateral  leaves,  and  in  some  cases  all  gradations  are  present  between 
these  lateral  leaves  on  the  axis  and  their  consolidation  into  an  ovuliferous 
scale.  In  the  normal  condition  of  the  ovuliferous  scale  the  axis  has  disap- 
peared and  the  shoot  is  represented  only  by  the  consolidated  leaves,  which 
would  represent  then  the 
macrosporophylls  (or  carpels) 
each  bearing  one  macrospo- 
rangium  (ovule). 

One  of  the  most  interesting 
and  plausible  views  is  that 
of  Celakovsky.  He  believes 
that  the  axial  shoot  is  reduced 
to  two  ovules,  that  the  ovules 


Fig.  362. 

Pine  seed,  section  of.  sc, 
seed  coat ; «,  remains  of  nu- 
cellus ;  end,  endosperm 
(  =  female  gametophy  te ) ; 
emb,  embryo  =  young  spo- 
rophyte.  Seed  coat  and 
nucellus=  remains  of  old 
sporophyte. 


Fig.  363- 
Embryo  of  white 
pine  removed  from 
seed,  showing 
several  cotyle- 
dons. 


?%ri 
i^^aswtea 

"Ipt^ 
!*Ore£&Trai' 


Fig.  364. 

Pine  seedling  just 
emerging  from  the 
ground. 


have  two  integuments,  but  the  outer  integument  of  each  has  become  pro- 
liferated into  scales  which  are  consolidated.  In  this  proliferation  of  the 
outer  integument  it  is  thrown  off  from  the  ovule  so  that  it  only  remains 
attached  to  one  side  and  the  larger  part  of  the  ovule  is  thus  left  with  only 
one  integument.  This  view  is  supported  by  the  fact  that  in  gingko,  for 
example  (another  gymnosperm),  the  outer  integument  (the  "collar") 
sometimes  proliferates  into  a  leaf.  Celakovsky's  view  is,  therefore,  not 
very  different  from  the  second  one  mentioned  above. 


MORPHOLOG  ¥. 


Fig.  365. 
White-pine  seedling  casting  seed  coats. 


CHAPTEk  XXXIV. 

FURTHER  STODGES  ON  GYMNOSPERMS. 
Cycas. 

627.  In  such  gymnosperms  as  cycas,  illustrated  in  the  front- 
ispiece, there  is  a  close  resemblance  to  the  members  of  the  fern 

group,  especially  the  ferns  themselves. 
This  is  at  once  suggested  by  the  form  of 
the  leaves.  The  stem  is  short  and  thick. 
The  leaves  have  a  stout  midrib  and 
numerous  narrow  pinnae.  In  the  center 
of  this  rosette  of  leaves  are  numerous 
smaller  leaves,  closely  overlapping  like 
bud  scales.  If  we  remove  one  of  these 
at  the  time  the  fruit  is  forming  we  see  that 
in  general  it  conforms  to  the  plan  of  the 
large  leaves.  There  are  a  midrib  and  a 
number  of  narrow  pinnae  near  the  free 
end,  the  entire  leaf  being  covered  with 
woolly  hairs.  But  at  the  lower  end,  in 

of    Cyczis 

revoiuta.  These  are  the    macrosporangia  (ovules) 

of  cycas,  and  correspond  to  the  macrosporangia  of  selaginella, 
and  the  leaf  is  the  macrosporophyll. 

628.  Female  prothallium  of  cycas.— In   figs.  367,  368,  are 
shown  mature  ovules,  or  macrosporangia,  of  cycas.     In  368,  which 
is  a  roentgen-ray  photograph  of  367,  the  oval  prothallium  can  be 
seen.     So  in  cycas,  as  in  selaginella,  the  female  prothallium  is 

3" 


312 


MORPHOLOGY. 


developed  entirely  inside  of  the  macrosporangium,  and  derives 
the  nutriment  for  its  growth  from  the  cycas  plant,  which  is  the 


Fig.  367.  Fig.  368. 

Macrosporangium  of  Cycas  revoluta         Roentgen  photograph  of  same,  show- 

ing female  prothallium. 

sporophyte.     Archegonia  are  developed  in  this  internal  mass  of 

cells.     This  aids  us  in  deter- 

mining that  it  is  the  prothal- 

lium.   In  cycas  it  is  also  called 

endosperm,    just    as    in    the 

pines. 


629.  If  we  cut  open  one  of  the 
mature  ovules,  we  can  see  the  en- 
dosperm (prothallium)  as  a  whitish 
mass  of  tissue.     Immediately  sur- 
rounding it  at  maturity  is  a  thin, 
papery  tissue,  the   remains  of  the 
nucellus    (macrosporangium),    and 
outside  of  this  are  the  coats  of  the 
ovule,  an  outer  fleshy  one  and  an 
inner  stony  one. 

630.  Microspores,  or  pollen,  of 
cycas.  —  The  cycas  plant  illustrated 
in  the  frontispiece  is  a  female  plant. 

Male  plants   also   exist  which  have 

,,  ,  ,  ,        . 

small  leaves  in  the  center  that  bear*  open  sporangia 


Kig. 


A  sporophyll  (stamen)  of  cycas  ;  sporangia  in 
groups  on  the  under  side,  b,  group  of  sporangia  : 
*  (From  Warming.) 


FURTHER   STUDIES    ON   GYMNOSPERMS. 


313 


only  microsporangia.  These  leaves,  while  they  resemble  the  ordinary  leaves, 
are  smaller  and  correspond  to  the  stamens.  Upon 
the  under  side,  as  shown  in  fig.  369,  the  microspo- 
rangia are  borne  in  groups  of  three  or  four,  and  these 
contain  the  microspores,  or  pollen  grains.  The  ar- 
rangement of  these  microsporangia  on  the  under  side 
of  the  cycas  leaves  bears  a  strong  resemblance  to  the 
arrangement  of  the  sporangia  on  the  under  side  of 
the  leaves  of  some  ferns. 

631.  The  gingko  tree  is 
another  very  interesting  plant 
belonging  to  this  same  group. 
It  is  a  relic  of  a  genus  which  \  B  I R  Fig.  370. 

Zamia  inte- 
grifolia,show- 
in  g  thick 
stem,  fern-like 
leaves,  and 
cone  of  male 
flowers. 


flourished  in  the  remote 
past,  and  it  is  interesting 
also  because  of  the  re- 
semblance of  the  leaves 
to  some  of  the  ferns  like 
adiantum,  which  sug- 
gests that  this  form  of 
the  leaf  in  gingko  has 
been  inherited  from  some 
fern-like  ancestor. 

632.  While  the  resem- 
blance of  the  leaves  of 
so  me  of  the  gymnosperms 
to  those  of  the  ferns  sug- 
gests fern-like  ancestors 
for  the  members  of  this 
group,  there  is  stronger 
evidence  of  such  ances- 
try in  the  fact  that  a  pro- 
thallium  can  well  be  de- 
(After  termined  in  the  ovules. 
The  endosperm  with  its 


Fig.  371. 

Two  spermatozoids  in  end  of  pollen  tube  of  cycas. 
drawing  by  Hirase  and  Ikeno.) 


well-formed  archegonia  is  to  be  considered  a  prothallium. 

633.  Spermatozoids   in  some    gymnosperms. — But  within  the   past  two 
years  it  has  been  discovered  in  gingko,  cycas,  and  zamia,  all  belonging  to  this 


314 


MORPHOLOG  Y. 


cycas, 

small  spermatozoid  fusing 
with  the  larger  female  nu- 
cleus  of  the  egg  The  egg 


Hirase  and  Ikeno.) 


group,  that  the  sperm  cells  are  well-formed  spermatozoids.  In  zamia  each 
one  is  shaped  somewhat  like  the  half  of  a  biconvex  lens,  and  around  the  con- 
vex surface  are  several  coils  of  cilia.  After  the 
pollen  tube  has  grown  down  through  the  nucel- 
lus,  and  has  reached  a  depression  at  the  end  of 
the  prothallium  (endosperm)  where  the  arche- 
gonia  are  formed,  the  spermatozoids  are  set 
free  from  the  pollen  tube,  swim  around  in  a 
liquid  in  this  depression,  and  later  fuse  with 
the  egg.  In  gingko  and  cycas  these'  spermato- 
zoids were  first  discovered  by  Ikeno  and  Hirase 
in  Japan,  and  later  in  zamia  by  Webber  in  this 
country.  In  figs.  371-374  the  details  of  the 
male  prothallia  and  of  fertilization  are  shown. 

634.  The  sporophyte  in  the  gymnosperms.  — 
In  the  pollen  grains  of  the  gymnosperms  we 
easily  recognize  the  characters  belonging  to  the 

SP°reS  in  the  femS  and  thdr  allies'  as  Wel1  as  in 
the  liverworts  and  mosses.     They  belong  to  the 

,  ,  ., 

same  series  of  organs,  are  borne  on  the  same 

phase  or  generation  of  the  plant>  and  are  ?racti- 

cally  formed  in  the  same  general  way,  the 
variations  between  the  different  groups  not  being  greater  than  those  within 
a  single  group.  These  spores  we  have  recognized  as  being  the  product  of 
the  sporophyte.  We  are  able  then  to  identify  the  sporophyte  as  that  phase 
or  generation  of  the  plant  formed  from  the  fer- 
tilized egg  and  bearing  ultimately  the  spores. 
We  see  from  this  that  the  sporophyte  in  the 
gymnosperms  is  the  prominent  part  of  the 
plant,  just  as  we  found  it  to  be  in  the  ferns. 
The  pine  tree,  then,  as  well  as  the  gingko,  cycas, 
yew,  hemlock-spruce,  black  spruce,  'the  giant 
redwood  of  California,  etc.,  are  sporophytes. 

While  the  sporangia  (anther  sacs)  of  the  male 
flowers  open  and  permit  the  spores  (pollen)  to  be  scattered,  the  sporangia  of 
the  female  flowers  of  the  gymnosperms  rarely  open.  The  macrospore  is  de- 
veloped within  sporangium  (nucellus)  to  form  the  female  prothallium  (en- 
dosperm). 

635.  The  gametophyte  has  become  dependent  on  the  sporophyte.  —  In  this 
respect  the  gymnosperms  differ  widely  from  the  pteridophytes,  though  we  see 
suggestions  of  this  condition  of  things  in  Isoetes  and  Selaginella,  where  the  fe- 
male prothallium  is  developed  within  the  macrospore,  and  even  in  Selaginella 
begins,  and  nearly  completes,  its  development  while  still  in  the  sporangium. 


Fig"  373< 


tail. 


(After    Ikeno    and 


FUR  THER   STUD TES   ON  G  YMNOSPERMS.          3  1 5 

In  comparing  the  female  prothallium  of  the  gymnosperms  with  that  of  the 
fern  group  we  see  a  remarkable  change  has  taken  place.     The  female  pro- 
thallium  of  the  gymno- 

Er     ^2  ID  sperms     is    very    much 

^        -,  I         !         reduced  in  size.      Espe- 

cially, it  no  longer  leads 
an  independent  existence 
from  the  sporophyte,  as 
is  the  case  with  nearly 
all  the  fern  group.  It 
remains  enclosed  within 
the  macrosporangium  (in 
cycas  if  not  fertilized  it 
sometimes  grows  outside 
of  the  macrosporangium 
and  becomes  green),  and 
derives  its  nourishment 
through  it  from  the  sporo- 
phyte, to  which  the  latter 
remains  organically  con- 
nected. This  condition 
of  the  female  prothallium 
of  the  gymnosperms 
necessitated  a  special 


Fig.  374- 


Gingko  biloba.  A,  mature  pollen  grain;  B,  germinating  adaptation  of  the  male 
pollen  grain,  the  branched  tube  entering  among  the  cells  nrn*unii:lltn  ;n  orrW  rW 
of  the  nucellus;  Ex,  exine  (outer  wall  of  spore);,  J>lt  pro-  Pr° 

thallial  cell ;  />„,  antheridial  cell  (divides  later  to  form  stalk    the  sperm  cells  may  reach 
cell  and  generative  cell) ;  /'a,  vegetative  cell ;   Krt,vacuoles;  JT 

Nc,  nucellus.     (After  drawings  by  Hirase  and  Ikeno.)  and  fertilize  the  egg  cell. 


Fig.  375- 

Gingko  biloba,  diagrammatic  representation  of  the  relation  of  pollen  tube  to  the  arche* 
gonium  in  the  end  of  the  nucellus.  pt,  pollen  tube ;  o,  archegonium.  (After  drawing  by 
Hirase  and  Ikeno.) 


636.   Gymnosperms  are  naked  seed  plants. — The  pine,  as  we  have  seen, 
has  naked  seeds.     That  is,  the  seeds  are  not  enclosed  within  the  carpel,  but 


MORPHOLOG  Y. 


are  exposed  on  the  outer  surface.     All  the  plants  of  the  great  group  to 

which  the  pine  belongs  have 
naked  seeds.  For  this  reason 
the  name  "  gymno  sperms" 
has  been  given  to  this  great 
group. 

637.  Classification  of  gymno  - 
sperms. — The  gingko  tree  has 
until  recently  been  placed  with 
the  pines,  yew,  etc.,  in  the  order 
Fig.  377.  Finales,  but  the  discovery  of 

Spermatozoid  of  za-    the  spermatozoids  in  the  pollen 
mia      showing     spiral        ,  ... 

row  of   cilia.      (After    tube    suggests    that    it    is    not 
Webber.)  closely  allied  with  the  Finales, 

and  that  it  represents  an  order 

Engler  arranges  the  living  gymnosperms  somewhat 


Fig.  376. 

Spermatozoids  of 
zamia  in  pollen  tube; 
pg,  pollen  grain;  a,  a, 
spermatozoids.  (After 
Webber.) 


coordinate  with  them, 
as  follows: 


Class  Gymnospermae. 


Order  i.     Cycadales;   family  Cycadaceae.     Cycas,  Zamia,  etc. 
Order  2.     Gingkoales;   family  Gingkoaceae.     Gingko. 

Order  3.     Finales  (or  Coniferae);  family  i.  Taxaceae.     Taxus,    the   common 

yew  in  the  eastern  United 
States,  and  Torreya,  in  the 
western  United  States,  are 
examples. 

family  2.  Pinaceae.  Sequoia  (redwood  of 
California),  firs,  spruces,  pines, 
cedars,  cypress,  etc. 

Order  4.  Gnetales.  Welwitschia  mirabilis,  deserts  of  southwest  Africa; 
Ephedra,  deserts  of  the  Mediterranean  and  of  West 
Asia.  Gnetum,  climbers  (Lianas),  from  tropical 
Asia  and  America. 


ANGIOSPERMS:    TRILLIUM. 
641.  Corolla. — Next  above  the  calyx  is  a  whorl  of  white  or 


pinkish  members,  in 
are  also  leaf-like  in  form, 
being  usually  somewhat 
make  up  what  is  the 
and  each  member  of  the 
they  are  parts  of  the 
their  form  and  posi- 
also  belong  to  the  leaf 
642.  Androacium.  — 
tion  of  the  corolla  is 
of  members  which  do  not 
form.  They  are  known 
As  seen  in  fig.  379  each 
ament),  and  extending 
greater  part  of  the  length 
side.  This  part  of  the 
ridges  form  the  anther 
Soon  after  the  flower  is 
ther  sacs  open  also  by  a 
along  the  edge  of  the 
time  we  see  quantities  of 


Trillium  grand! florum,  which 
and  broader  than  the  sepals, 
broader  at  the  free  end.  These 
corolla  in  the  higher  plants, 
corolla  is  a  petal.  But  while 
flower,  and  are  not  green, 
tion  would  suggest  that  they 
series. 

Within  and  above  the  inser- 
found  another  tier,  or  whorl, 
at  first  sight  resemble  leaves  in 
in  the  higher  plants  as  stamens. 
stamen  possesses  a  stalk  (  =  fil- 
along  on  either  side  for  the 
are  four  ridges,  two  on  each 
stamen  is  the  anther,  and  the 
sacs,  or  lobes, 
opened,  these  an- 
split  in  the  wall 
ridge.  At  this 


Fig  378.  yellowish   powder 

or  dust  escaping  from  the     Trillium  grandiflorum.       ruptured      anther 
locules,      If  we  place  some  of  this  under  the  microscope  we  see 


320 


MORPHOLOGY. 


that  it  is  made  up  of  minute  bodies  which  resemble  spores ;  they 
are  rounded  in  form,  and  the  outer  wall  is  spiny.     They  are  in  fact 

spores,  the  microspores 
of  the  trillium,  and  here, 
as  in  the  gymnosperms, 
are  better  known  as  pollen. 


Fig.  379. 

Sepal,  petal,  stamen,  and  pistil  of  Trillium 
grandinorum. 

643.  The  stamen  a  sporo- 
phyll. — Since     these     pollen 
grains  are  the  spores,  we  would^ 
infer,     from     what    we     have 
learned  of  the  ferns  and  gym- 
nosperms, that  this  member  of 

the  flower  which  bears   them  is  a  sporophyll ; 

and  this  is  the  case      It  is  in  fact  what  is  called 

the  micro  sporophyll.     Then  we  see  also  that  the 

anther  sacs,  since  they  enclose  the  spores,  would 

be  the  sporangia  (microsporangia).      From  this 

it  is  now  quite  clear  that  the  stamens 

belong  also  to  the  leaf  series.     They 

are  just  six  in  number,  twice  the  number 

found  in  a  whorl  of  leaves,  or  sepals, 

or  corolla.     It  is  believed,   therefore, 

that  there  are  two  whorls  of  stamens  in  the  flower  of  trillium. 

644.  Gynoecium. — Next  above  the  stamens  and  at  the  center 
of  the  flower  is  a  stout,  angular,  ovate  body  which  terminates  in 
three  long,  slender,  curved  points.     This  is  the  pistil,  and  at 


Fig.  380. 

Trillium  gran- 

diflorum,     with 

the     compound 

Gistil  expanded 
ito  three  leaf- 
like  members. 
At  the  right 
these  three  are 
shown  in  detail. 


ANGIOSPERMS:    TRILLIUM. 


321 


present  the  only  suggestion  which  it  gives  of  belonging  to  the 
leaf  series  is  the  fact  that  the  end  is  divided  into  three  parts,  the 
number  of  parts  in  each  successive  whorl  of  members  of  the 
flower.  If  we  cut  across  the  body  of  this  pistil  and  examine  it 
with  a  low  power  we  see  that  there  are  three  chambers  or  cavi- 
ties, and  at  .the  junction  of  each 
the  walls  suggest  to  us  that  this 
body  may  have  been  formed  by  the 
infolding  of  the  margins  of  three 
leaf- like  members,  the  places  of 
contact  having  then  become  grown 
together.  We  see  also  that  from 
the  incurved 


Fig.  381. 

Abnormal 
trillium.  The 
nine  parts  of 
the  perianth 
are  green, 
and  the  outer 
whorls  of 
stamens  are 
expanded  into 
petal  -like 
members. 


margins  of  each 
division  of  the 
pistil  there  stand 

out  in  the  cavity  oval  bodies. 
These  are  the  ovules.  Now  the 
ovules  we  have  learned  from  our 
study  of  the  gymnosperms  are  the 
sporangia  (here  the  macrosporangia). 
It  is  now  more  evident  that  this  curious  body,  the  pistil,  is  made  up 
of  three  leaf-like  members  which  have  fused  together,  each  mem- 
ber being  the  equivalent  of  a  sporophyll  (here  the  macrosporo- 
phyll) .  This  must  be  a  fascinating  observation,  that 
plants  of  such  widely  different  groups  and  of  such 
different  grades  of  complexity  should  have  members 
formed  on  the  same  plan  and  belonging  to  the  same 
series  of  members,  devoted  to  similar  functions,  and 
yet  carried  out  with  such  great  modifications  that  at 
first  we  do  not  see  this  common  meeting  ground 
which  a  comparative  study  brings  out  so  clearly. 

645.   Transformations  of  the  flower  of  trillium.— 
antherS'Knef   If  anything  more  were  needed  to  make  it  clear  that 

on  the  margin.     ^  parts  Qf  ^  ^^  Qf  triUium  belong    to  the    leaf 

series  we  could  obtain  evidence   from  the  transformations  which 


Fig.  382. 
Transformed 
stamen  of  tril- 


322 MORPHO  L  OG  Y. 

the  flower  of  trillium  sometimes  presents.  In  fig.  381  is  a  sketch 
of  a  flower  of  trillium,  made  from  a  photograph.  One  set  of 
the  stamens  has  expanded  into  petal -like  organs,  with  the  anther 
sacs  on  the  margin.  In  fig.  380  is  shown  a  plant  of  Trillium 
grandiflorum  in  which  the  pistil  has  separated  into  three  distinct 
and  expanded  leaf-like  structures,  all  green  except  portions  of 
the  margin. 


Dentaria. 

646.  General  appearance. — For  another  study  we  may  take 
a  plant  which  belongs  to  another  division  of  the  higher  plants, 
the    common     "pepper    root,"    or    "  toothwort "    (Dentaria 
diphylla)  as  it  is  sometimes  called.     This  plant  occurs  in  moist 
woods  during  the  month  of  May,  and  is  well  distributed  in  the 
northeastern  United  States.     A  plant  is  shown  in  fig.  383.      It 
has  a  creeping  underground  rhizome,  whitish  in  color,  fleshy, 
and  with  a  few  scales.     Each  spring  the  annual  flower-bearing 
stem  rises  from  one  of  the  buds  of  the  rhizome,  and  after  the 
ripening  of  the  seeds,  dies  down. 

The  leaves  are  situated  a  little  above  the  middle  point  of  the 
stem.  They  are  opposite  and  the  number  is  two,  each  one 
being  divided  into  three  dentate  lobes,  making  what  is  called  a 
compound  leaf. 

647.  Parts  of  the  flower. — The  flowers  are  several,  and  they 
are  borne  on  quite  long  stalks  (pedicels)  scattered  over  the  ter- 
minal portion  of  the  stem.     We  should  now  examine  the  parts 
of  the  flower  beginning  with  the  calyx.     This  we  can  see,  look- 
ing at  the  under  side  of  some  of  the  flowers,  possesses  four  scale- 
like  sepals,  which  easily  fall  away  after  the  opening  of  the  flower. 
They  do  not  resemble  leaves  so  much  as  the  sepals  of  trillium, 
but  they  belong  to  the  leaf  series,  and  there  are  two  pairs  in  the 
set  of  four.    The  corolla  also  possesses  four  petals,  which  are  more 
expanded  than  the  sepals  and  are  whitish  in  color.     The  sta- 
mens are  six  in  number,  one  pair  lower  than  the  others,  and  also 


ANCIOSPERMS:    DENTARIA.  323 

shorter.      The  filament  is  long  in  proportion  to  the  anther,  the 


latter  consisting  of  two 
lobes  or  sacs,  instead  of 
four  as  in  trillium.  The 
pistil  is  composed  of  two 
carpels,  or  leaves  fused 
together.  So  we  find  in 
the  case  of  the  pepper 
root  that  the  parts  of  the 
flower  are  in  twos,  or 
multiples  of  two.  Thus 
they  agree,  in  this  respect 
with  the  leaves;  and 
while  we  do  not  see 
such  a  strong  resem- 
blance between  the 
parts  of  the  flower 
here  and  the  leaves, 
yet  from  the  pres- 
ence of  the  pollen 


Fig.  384. 

Flower  of  the  toothwort  (Dentaria 
diphylla). 


Fig-383. 
Toothwort  (Dentaria  diphylla). 


324 


MORPHOLOG  Y. 


(microspores)  in  the  anther  sacs  (microsporangia)  and  of  ovules 
(macrosporangia)  on  the  margins  of  each  half  of  the  pistil,  we 
are,  from  our  previous  studies,  able  to  recognize  here  that  all  the 
members  of  the  flower  belong  to  the  leaf  series. 

648.  In  trillium  and  in  the  pepper  root  we  have  seen  that  the 
parts  of  the  flower  in  each  apparent  whorl  are  either  of  the  same 
number  as  the  leaves  in  a  whorl,  or  some  multiple  of  that  num- 
ber. This  is  true  of  a  large  number  of  other  plants,  but  it  is  not 
true  of  all.  A  glance  at  the  spring  beauty  (Claytonia  virginiana, 
and  at  the  anemone  (or  Isopyrum  biternatum,  fig.  563)  will 
serve  to  show  that  the  number  of  the  different  members  of  the 
flower  may  vary.  The  trillium  and  the  dentaria  were  selected 
as  being  good  examples  to  study  first,  to  make  it  very  clear  that 
the  members  of  the  flower  are  fundamentally  leaf  structures,  or 
rather  that  they  belong  to  the  same  series  of  members  as  do  the 
leaves  of  the  plant. 

649.  Synopsis  of  members  of  the  sporophyte  in  angiosperms. 

Higher  plant. 
Sporophyte  phase 

(or  modern  phase).  Leaf 


Foliage  leaves. 
Perianth  leaves. 
Spore-bearing  leaves 

with  sporangia. 
(Sporangia  sometimes 

on  shoot.) 


Flower. 


CHAPTER    XXXVI. 


GAMETOPHYTE  AND  SPOROPHYTE  OF  ANGIO- 
SPERMS. 

650.  Male  prothallium  of  angiosperms. — The  first  division 
which  takes  place  in  the  nucleus  of  the  pollen  grain  occurs,  in 
the  case  of  trillium  and  many  others  of  the  angio- 
sperms, before  the  pollen  grain  is  mature.  In  the 
case  of  some  specimens  of  T.  grandiflorum  in 
which  the  pollen  was  formed  during  the  month 
of  October  of  the  year  before  flowering,  the  divi- 
sion of  the  nucleus  into  two  nuclei  took  place 
soon  after  the  formation  of  the  four  cells  from 
the  mother  cell.  The  nucleus  divided  in  the 
young  pollen  grain  is  shown  in  fig.  385.  After  this  takes 
place  the  wall  of  the  pollen  grain  becomes  stouter,  and  minute 
spiny  projections  are  formed. 

651.  The  larger  cell  is  the  vegetative  cell 
of  the  prothallium,  while  the  smaller  one,  since 
it  later  forms  the  sperm  cells,  is  the  generative 
cell.  This  generative  cell  then  corresponds 
to  the  central  cell  of  the  antheridium,  and  the 
vegetative  cell  perhaps  corresponds  to  a  wall  F- 

cell  of  the  antheridium.     If  this  is  so,  then  the      Germinating  spores 

male  prothallium  of  angiosperms  has  become  (Poljen  grains)  of  pel- 

tandra ;        generative 

reduced  to  a  very  simple  antheridium.     The  nuclens  in  one  undi- 
e      ,  .        ,  c         ,..,..          vided,  in  other  divided 

farther  growth  takes  place  after  fertilization,   to  form  the  two  sperm 


Fig-  385. 
Nearly  mature 
pollen  grain  of  tril- 
lium.  The  smaller 
cell  is  the  genera- 
tive cell. 


In  some  plants  the  generative  cell  divides  into 
the  two  sperm  cells  at  the  maturity  of  the  pollen  grain, 
pollen  grain.  In  other  cases  the  generative  cell  divides  in  the  pollen  tube 
after  the  germination  of  the  pollen  grain.  For  study  of  the  pollen  tube  the 
pollen  may  be  germinated  in  a  weak  solution  of  sugar,  or  on  the  cut  surface 

325 


326 


MORPHOLOG  Y. 


of  pear  fruit,  the  latter  being  kept  in  a  moist  chamber  to  prevent  drying 
the  surface. 

652.  In  the  spring  after  flowering  the  pollen  escapes  from  the  anther  sacs, 
and  as  a  result  of  pollination  is  brought  to  rest  on  the  stigma  of  the  pistil. 
Here  it  germinates,  as  we  say,  that  is,  it  develops  a  long  tube  which  makes 
its  way  down  through  the 
style,  and  in  through  the 
micropyle  to  the  embryo  sac, 
where,  in  accordance  with 
what  takes  place  in  other 
plants  examined,  one  of  the 
sperm  cells  unites  with  the 
egg,  and  fertilization  of  the 
egg  is  the  result. 


653.  Macrospore  and  embryo  sac. 

three  carpels  are  united  into  one, 
two  carpels  are  also  united  into  one 
Simple  pistils  are  found  in  many 
in  the  ranunculaceae,  the  buttercups, 
These  simple  pistils  bear  a  greater 


— In  trillium  the 
and  in  dentaria  the 
compound  pistil, 
plants,  for  example 
columbine,  etc. 
resemblance  to  a 
leaf,  the  margins  of 
which  are  folded 
around  so  that  they 
meet  and  enclose 
the  ovules  or  spo- 
rangia. 

654.  If  we  cut 
across  the  com- 
pound pistil  of  tril" 
Hum  we  find  that 
the  infoldings  of  the 
Fig.  387.  Y  [  ^  three  pistils  meet  to 

Section  of  pistil  of  tril-  Fig.  388.  , 

Hum,  showing  position  of  Mandrake  (Podo-   IOrm    three    partial 

ovules  (macrosporangia).  phyllum  peltatum).         rfitions          which 

extend  nearly  to  the  center,  dividing  off  three  spaces.  In  these 
spaces  are  the  ovules  which  are  attached  to  the  infolded  margins. 
If  we  make  cross  sections  of  a  pistil  of  the  May-apple  (podo- 


GAMETOPHYTE  AND    SPOROPHYTE. 


327 


phyllum)  and  through  the  ovules  when  they  are  quite  young,  we 
shall  find  that  the  ovule  has  a  structure  like  that  shown  in  fig.  389. 
At  m  is  a  cell  much  larger  than  the  surrounding  ones.  This  is 
called  the  macrospore.  The  tissue  surrounding  it  is  called  here  the 
nucellus,  but  because  it  contains  the  macrospore  it  must  be  the 
macrosporangium.  The  two  coats  or  integuments  of  the  ovule  are 
yet  short  and  have  not  grown  out  over  the  end  of  the  nucellus. 
This  macrospore  increases  in  size,  forming  first  a  cavity  or  sac 
in  the  nucellus,  the  embryo  sac.  The  nucleus  divides  several 


Fig.  389. 

Young  ovule  (macrosporangium)  of  podophyllum.    n,  nucellus  containing  the  one- 
celled  stage  of  the  macrospore;    i.int,  inner  integument;    o.int,  outer  integument. 

times  until  eight  are  formed,  four  in  the  micropylar  end  of  the 
embryo  sac  and  four  in  the  opposite  end.  In  some  plants  it 
has  been  found  that  one  nucleus  from  each  group  of  four  moves 
toward  the  middle  of  the  embryo  sac.  Here  they  fuse  together 
to  form  one  nucleus,  the  endosperm  nucleus  or  definitive  nucleus 
shown  in  fig.  390.  One  of  the  nuclei  at  the  micropylar  end  is 
the  egg,  while  the  two  smaller  ones  nearer  the  end  are  the  syner* 


328 


MORPHOLOG  Y. 


gids.  The  egg  cell  is  all  that  remains  of  the  archegonium  in 
this  reduced  prothallium.  The  three  nuclei  at  the  lower  end 
are  the  antipodal  cells. 


eggs 


Pig.  390. 

Podophyllum  peltatum,  ovule  containing  mature  embryo  sac;  two  synergids  and 
gs  at  lelt,  endosperm  nucleus  in  center,  three  antipodal  cells  at  right. 

655.  Embryo  sac  is  the  young  female  prothallium.—  In  figs. 
391-393  are  shown   the  different  stages  in  the  development  of 

the  embryo  sac  in  lilium.  The 
embryo  sac  at  this  stage  is  the 
young  female  prothallium,  and 
the  egg  is  the  only  remnant  of  the 
female  sexual  organ,  the  arche- 
gonium, in  this  reduced  gameto- 
phyte. 

656.  Fertilization.—  When  the 
pollen  tube  has  reached  the  em- 
bryo sac  (paragraph  652)  it  opens 

Macrospore  (one-celled  stage)  of  lilium.  and  the  two  Sperm  Cells  are  emptied 

near  the  egg.  The  first  sperm  nucleus  enters  the  protoplasm 
surrounding  the  egg  nucleus  and  uniting  with  the  latter  brings 
about  fertilization.  The  second  sperm  nucleus  often  unites 
with  the  endosperm  nucleus  (or  with  one  or  both  of  the  "polar 
nuclei"),  bringing  about  what  some  call  a  second  fertilization. 
Where  this  takes  place  in  addition  to  the  union  of  the  first  sperm 


Fig.  391. 


GAMETOPHYTE  AND    SPOROPHYTE. 


329 


nucleus  with  the  egg  nucleus  it  is  called  double  fertilization.  The 
sperm  nucleus  is  usually  smaller  than  the  egg  nucleus,  but  often 
grows  to  near  or  quite  the  size  of  the  egg  nucleus  before  union. 
See  figs.  394  and  395. 

657.  Fertilization  in  plants  is  fundamentally  the  same  as 
in  animals. — In  all  the  great  groups  of  plants  as  represented  by 
spirogyra,  oedogonium,  vaucheria,  peronospora,  ferns,  gymno- 


Fig.  392. 

Two-  and  four-celled  stage  of  embryo-sac  of  lilium.     The  middle  one  shows 
division  of  nuclei  to  form  the  four-celled  stage.     (Easter  lily.) 

sperms,  and  in  the  angiosperms,  fertilization,  as  we  have  seen, 
consists  in  the  fusion  of  a  male  nucleus  with  a  female  nucleus. 
Fertilization,  then,  in  plants  is  identical  with  that  which  takes 
place  in  animals. 

658.  Embryo. — After  fertilization  the  egg  develops  into  a  short 
row  of  cells,  the  suspensor  of  the  embryo.     At  the  free  end  the  em- 
bryo develops.     In  figs.  397  and  398  is  a  young  embryo  of  trillium. 

659.  Endosperm,  the  mature  female  prothallium. — During 
the  development  of  the  embryo  the  endosperm  nucleus  divides 


330 


MORPHOLOG  Y. 


into  a  great  many  nuclei  in  a  mass  of  protoplasm,  and  cell  walls 
are  formed  separating  them  into  cells.  This  mass  of  cells  is  the 
endosperm,  and  it  surrounds  the 
embryo.  It  is  the  mature  female 
prothallium,  belated  in  its  growth 
in  the  angiosperms,  usually  de- 
veloping only  when  fertilization 
takes  place,  and  its  use  has  been 
assured. 

660.    Seed. — As    the    embryo 


Fig-  393- 


Fig-  394- 


Mature  embryo  sac  (young  pro- 
tnallium)  of  lilium.    m,  micropylar 

end ;   S,  synergids ;   E,   egg ;  Pn,       egg;  S,  synergids;  P,  pollen 
polar    nuclei ;    A  ntt    antipodals.       the  end.    (Duggar.) 
(Easter  lily.) 


Section  through  nucellus  and  upper  part  of  embryo 
sac  of  cotton  at  time  of  entrance  of  pollen  tube.     E, 
tube  with  sperm  cell  in 


GAMETOPIIYTE   AND    SPOROPHYTE. 


33  l 


is  developing  it  derives  its  nourishment  from  the  endosperm  (or 
in  some  cases  perhaps  from  the  nucellus).     At  the  same  time 


-J5 


Fertilization  of  cotton.  fit, 
pollen  tube  ;  Sn,  synergids  ;  /: , 
egg,  with  male  and  female  nu- 
cleus fusing.  (Duggar.) 

the  integuments  increase 
in  extent  and  harden  as 
the  seed  is  formed. 

661.  Perisperm.  —  In 
most  plants  the  nucellus  is 
all  consumed  in  the  devel- 
opment of  the  endosperm, 
so  that  only  minute  frag- 
ments of  disorganized  cell 
walls  remain  next  the  in- 
ner integument.     In  some 
plants,  however,  (the  water- 
lily    family,    the    pepper  Fig.  396. 

Diagrammatic  section  of  ovary  and  ovule  at  time 

family,   etc.,)  a   portion  Of    of  fertilization  in  angiosperm     y;  funicle  of  ovule; 

n,  nucellus;    m,  micropyle ;   b,   antipodal  cells  of 

the  nucellus  remains  in- 
tact in  the  mature  seed. 
In  such  seeds  the  remain- 
ing portion  of  the  nucellus  is  the  perisperm. 

662.  Presence   or  absence  of  endosperm  in  the  seed. — In 
many  of  the  angiosperms  all  of  the  endosperm  is  consumed  by 
the  embryo  during  its  growth  in  the  formation  of  the  seed.    This 
is  the  case  in  the  rose  family,  crucifers,  composites,  willows,  oaks, 
legumes,  etc.,  as  in  the  acorn,   the  bean,  pea  and  others.     In 
some,  as  in  the  bean,  a  large  part  of  the  nutrient  substance  pass- 


, 

n-  embrvo  sac  ;  *»  endosperm  nucleus ;  A,  egg  cell  and 
synergids  ;  at,  outer  integument  of  ovule  ;  ii,  inner 
jptegument.  The  track  of  the  pollen  tube  is  shown 
down  through  the  style,  walls  of  the  ovary  to  the 
micropylar  end  of  the  embryo  sac. 


332 


MORPHOLOG  Y. 


ing  from  the  endosperm  into  the  embryo  is  stored  in  the  cotyle- 
dons for  use  during  germination.    In  other  plants  the  endosperm 


Fig.  397-  Fig.  398. 

Section  of  one  end  of  ovule  of  trillium,  showing  Embryo     en- 

young  embryo  in  endosperm.  larged. 

is  not  all  consumed  by  the  time  the  seed  is  mature.     Examples  of 
Ihis  kind  are  found  in  the  buttercup  family,  the  violet,  lily,  palm, 


Fig.  399. 

Seed  of  violet,  external  view,  and 
section.  The  section  shows  the  embryo 
lying  in  the  endosperm. 


PC 


Fig.  400. 

Section  of  fruit  of  pepper  (Piper 
nigrum),  showing  small  embryo  lying 
in  a  small  quantity  of  whitish  endo- 
sperm at  one  end,  the  perisperm  oc- 
cupying the  larger  part  of  the  interior, 
surrounded  by  pericarp. 


jack-in-the-pulpit,   etc.      Here  the  remaining  endosperm  in  the 
seed  is  used  as  food  by  the  embryo  during  germination. 
663.  Outer  parts  of  the  seed.— While  the  embryo  is  forming 


ANGIOSTERMS:   SEED.  333 

within  the  ovule  and  the  growth  of  the  endosperm  is  taking 
place,  where  this  is  formed,  other  correlated  changes  occur  in 
the  outer  parts  of  the  ovule,  and  often  in  adjacent  parts  of  the 
flower.  These  unite  in  making  the  "  seed, "  or  the  "  fruit. " 
Especially  in  connection  with  the  formation  of  the  seed  a  new 
growth  of  the  outer  coat,  or  integument,  of  the  ovule  occurs, 
forming  the  outer  coat  of  the  seed,  known  as  the  testa,  while 
the  inner  integument  is  absorbed.  In  some  cases  the  inner 
integument  of  the  ovule  also  forms  a  new  growth,  making  an 
inner  coat  of  the  seed  (rosaceae).  In  still  other  cases  neither 
of  the  integuments  develops  into  a  testa,  and  the  embryo  sac 
lies  in  contact  with  the  wall  of  the  ovary.  Again  an  additional 
envelope  grows  up  around  the  seed;  an  example  of  this  is 
found  in  the  case  of  the  red  berries  of  the  "  yew  "  (taxus),  the 
red  outer  coat  being  an  extra  growth,  called  an  aril. 

In  the  willow  and  the  milkweed  an  aril  is  developed  in  the 
form  of  a  tuft  of  hairs.  (In  the  willow  it  is  an  outgrowth  of 
the  funicle,  =  stalk  of  the  ovule,  and  is  called  a  funicular  aril; 
while  in  the  milkweed  it  is  an  outgrowth  of  the  micropyle,  = 
the  open  end  of  the  ovule,  and  is  called  a  micropylar  aril.) 

664.  Increase  in  size  during  seed  formation. — Accompany- 
ing this  extra  growth  of  the  different  parts  of  the  ovule  in  the 
formation  of  the  seed  is  an  increase  in  the  size,  so  that  the  seed 
is  often  much  greater  in  size  than  the  ovule  at  the  time  of  fer- 
tilization. At  the  same  time  parts  of  the  ovary,  and  in  many 
plants,  the  adherent  parts  of  the  floral  envelopes,  as  in  the  apple; 
or  of  the  receptacle,  as  in  the  strawberry;  or  in  the  involucre, 
as  in  the  acorn ;  are  also  stimulated  to  additional  growth,  and 
assist  in  making  the  fruit. 


334 


MORPHOLOGY. 


Ripened,  ovule.  « 


The  seed.  • 


665.  Synopsis  of  the  seed. 

Aril,  rarely  present. 

Ovular  coats  (one  or  two  usually  present),  the 

testa. 

Funicle  (stalk  of  ovule),  raphe  (portion  of 
funicle  when  bent  on  to  the  side  of  ovule), 
micropyle,   hilum    (scar   where   seed   was 
attached  to  ovary). 
Remnant   of   the   nucellus   (central   part   of 

ovule);   sometimes  nucellus  remains  as 
.  Peris  perm  in  some  albuminous  seeds. 
Endosperm,  present  in  albuminous  seeds. 

Embryo  within  surrounded  by  endosperm  when  this  is  present, 
or  by  the  remnant  of  nucellus,  and  by  the  ovular  coats  which 
make  the  testa.  In  many  seeds  (example,  bean)  the  endo- 
sperm is  transferred  to  the  cotyledons  which  become  fleshy 
(exalbuminous  seeds). 

666.  Parts  of  the  ovule.— In  fig.  401   are  represented  three 
different  kinds  of  ovules,  which  depend  on  the  position  of  the 


, 


ai 


Fig.  401. 

A,  represents  a  straight  (orthotropus)  ovule  of  polygonum;  B,  the  inverted 
(anatropous)  ovule  of  the  lily;  and  C,  the  right-angled  (campylotropus)  ovule  of 
the  bean,  f,  funicle;  c,  chalaza;  k,  nucellus;  at,  outer  integument;  ii,  inner 
integument;  m,  micropyle;  em,  embryo  sac. 

ovule  with  reference  to  its  stalk.  The  funicle  is  the  stalk  of  the 
ovule,  the  hilum  is  the  point  of  attachment  of  the  ovule  with 
the  ovary,  the  raphe  is  the  part  of  the  funicle  in  contact  with 
the  ovule  in  inverted  ovules,  the  chalaza  is  the  portion  of  the 
ovule  where  the  nucellus  and  the  integuments  merge  at  the  base 
of  the  ovule,  and  the  micropyle  is  the  opening  at  the  apex  of 
the  ovule  where  the  coats  do  not  meet. 


FLOWER:   MEMBERS  AND    ORGANS.  335 


Comparison  of  Organ  and  Member. 

667.  The  stamens  and  pistils  are  not  the  sexual  organs. — 

Before  the  sexual  organs  and  sexual  processes  in  plants  were 
properly  understood  it  was  customary  for  botanists  to  speak 
of  the  stamens  and  pistils  of  flowering  plants  as  the  sexual 
organs.  Some  of  the  early  botanists,  a  century  ago,  found  that 
in  many  plants  the  seed  would  not  form  unless  first  the  pollen 
from  the  stamens  came  to  be  deposited  on  the  stigma  of  the 
pistil.  A  little  further  study  showed  that  the  pollen  germinated 
on  the  stigma  and  formed  a  tube  which  made  its  way  down 
through  the  pistil  and  into  the  ovule. 

This  process,  including  the  deposition  of  the  pollen  on  the 
stigma,  was  supposed  to  be  fertilization,  the  stamen  was  looked 
on  as  the  male  sexual  organ,  and  the  pistil  as  the  female  sexual 
organ.  We  have  found  out,  however,  by  further  study,  and 
especially  by  a  comparison  of  the  flowering  plants  and  the  lower 
plants,  that  the  stamens  and  pistils  are  not  the  sexual  organs  of 
the  flower. 

668.  The  stamens  and  pistils  are  spore-bearing  leaves. — The 
stamen  is  the  spore-bearing  leaf,  and  the  pollen  grains  are  not 
unlike  spores;    in  fact  they  are  the  small  spores  of  the  angio- 
sperms.     The  pistil  is  also  a  spore-bearing  leaf,  the  ovule  the 
sporangium,  which  contains  the  large  spore  called  an  embryo  sac. 
In  the  ferns  we  know  that  the  spore  germinates  and  produces  the 
green    heart-shaped    prothallium.     The    prothallium    bears    the 
sexual  organs.     Now  the  fern  leaf  bears  the  spores  and  the  spore 
forms  the  prothallium.     So  it  is  in  the  flowering  plants.     The 
stamen  bears  the  small  spores — pollen  grains — and  the  pollen 
grain  forms  the  prothallium.     The  prothallium  in  turn  forms 
the  sexual  organs.     The  process  is  in  general  the  same  as  it  is  in 
the  ferns,  but  with  this  special  difference:    the  prothallium  and 
the  sexual  organ  of  the  flowering  plants  are  very  much  reduced. 

669.  Difference  between  organ  and  member.— While  it   is 
not  strictly  correct  then  to  say  that  the  stamen  is  a  sexual  organ, 


336  MORPHOLOG  y. 

or  male  organ,  we  might  regard  it  as  a  male  member  of  the  flower, 
and  we  should  distinguish  between  organ  and  member.  It  is  an 
organ  when  we  consider  pollen  production,  but  it  is  not  a  sexual 
organ.  When  we  consider  fertilization  it  is  not  a  sexual  organ, 
but  a  male  member  of  the  flower  which  bears  the  small  spore. 
The  following  table  will  serve  to  indicate  these  relations. 

Stamen  =  spore-bearing  leaf  =  male  member  of  flower. 

Anther  locule  =  sporangium. 

Pollen  grain   =  small   ,  spore = reduced     male     prothallium     and 
sexual  organ. 

So  the  pistil  is  not  a  sexual  organ,  but  might  be  regarded  as 
the  female  member  of  the  flower. 

Pistil  =  spore-bearing  leaf = female  member  of  flower. 

Ovule  =  sporangium. 

Embryo  sac = large    spore = female    prothallium    containing    the 

egg- 
The  egg       =a  reduced  archegonium=the  female  sexual  organ. 

Progression   and    Retrogression  in  Sporophyte  and 
Gametophyte. 

670.  Sporophyte  is  prominent  and  highly  developed.— In  the  angiosperms 
then,  as  we  have  seen  from  the  plants  already  studied,  the  trillium,  dentaria, 
etc.,  are  sporophytes,  that  is  they  represent  the  spore-bearing,  or  sporophytic, 
stage.  Just  as  we  found  in  the  case  of  the  gymnosperms  and  ferns,  this  stage 
is  the  prominent  one,  and  the  one  by  which  we  characterize  and  recognize  the 
plant.  We  see  also  that  the  plants  of  this  group  are  still  more  highly  special- 
ized and  complex  than  the  gymnosperms,  just  as  they  were  more  specialized 
and  complex  than  the  members  of  the  fern  group.  From  the  very  simple 
condition  in  which  we  possibly  find  the  Sporophyte  in  some  of  the  algae  like 
spirogyra,  vaucheria,  and  coleochaete,  there  has  been  a  gradual  increase  in 
size,  specialization  of  parts,  and  complexity  of  structure  through  the  bryo- 
phytes,  pteridophytes,  and  gymnosperms,  up  to  the  highest  types  of  plant 
structure  found  in  the  angiosperms.  Not  only  do  we  find  that  these  changes 
have  taken  place,  but  we  see  that,  from  a  condition  of  complete  dependence  of 
the  spore-bearing  stage  on  the  sexual  stage  (gametophyte),  as  we  find  it  in  the 
liverworts  and  mosses,  it  first  becomes  free  from  the  gametophyte  in  the  mem- 
bers of  the  fern  group,  and  is  here  able  to  lead  an  independent  existence. 
The  Sporophyte,  then,  might  be  regarded  as  the  modern  phase  of  plant  life, 


GAMETOPHYTE  AND   SPOROPHYTE.      -      337 

I 

since  it  is  that  which  has  become  and  remains  the  prominent  one  in  later 
times. 

671.  The  gametophyte  once  prominent  has  become  degenerate. — On  the 

other  hand  we  can  see  that  just  as  remarkable  changes  have  come  upon  the 
other  phase  of  plant  life,  the  sexual  stage,  or  gametophyte.  There  is  reason 
to  believe  that  the  gametophyte  was  the  stage  of  plant  life  which  in  early 
times  existed  almost  to  the  exclusion  of  the  sporophyte,  since  the  characteristic 
thallus  of  the  algae  is  better  adapted  to  an  aquatic  life  than  is  the  spore-bearing 
state  of  plants.  At  least,  we  now  find  in  the  plants  of  this  group  as  well  as  in 
the  liverworts,  that  the  gametophyte  is  the  prominent  stage.  When  we  reach  the 
members  of  the  fern  group,  and  the  sporophyte  becomes  independent,  we  find 
that  the  gametophyte  is  decreasing  in  size,  in  the  higher  members  of  thepteri- 
dophytes,  the  male  prothal  ium  consisting  of  only  a  few  cells,  while  the  fe- 
male prothallium  completes  its  development  still  within  the  spore  wall.  And 
in  selaginella  it  is  entirely  dependent  on  the  sporophyte  for  nourishment. 

672.  As  we  pass  through  the  gymnosperms  we  find  that  the  condition  of 
things  which  existed  in  the  bryophytes  has  been  reversed,  and  the  gameto- 
phyte is  now  entirely  dependent  on  the  sporophyte  for  its  nourishment,  the 
female  prothallium  not  even  becoming  free  from  the  sporangium,  which  remains 
attached  to  the  sporophyte,  while  the  remnant  of  a  male  prothallium,  during 
the  stage  of  its  growth,  receives  nourishment  from  the  tissues  of  the  nucellus 
through  which  it  bores  its  way  to  the  egg-cell. 

673.  In  the  angiosperms  this  gradual  degradation  of  the  male  and  female 
prothallia  has  reached  a  climax  in  a  one-celled  male  prothallium  with  two 
sperm-cells,  and  in  the  embryo-sac  with  no  clearly  recognizable  traces  of  an 
archegonium  to  identify  it  as  a  female  prothallium.     The  development  of  the 
endosperm  subsequent,  in  most   cases,  to  fertilization,  providing  nourishment 
for  the  sporophytic  embryo  at  one  stage  or  another,  is  believed  to  be  the  last 
remnant  of  the  female  prothallium  in  plants. 

674.  The  seed. — The  seed  is  the  only  important  character  possessed  by 
the  higher  plants  (the  gymnosperms  and  angiosperms)  which  is  not  pos- 
sessed by  one  or  another  of  the  lower  great  groups.     With  the  gradual  evo- 
lution of  the  higher  plants  from  the  lower  there  has  been  developed  at  cer- 
tain periods  organs  or  structural  characters  which  were  not  present  in  some 
of  the  lower  groups.     Thus  the  thallus  is  the  plant  body  of  the  algae  and 
fungi,  so  that  these  two  groups  of  plants  are  sometimes  called  Thattophytes. 
In  the  Bryophytes  (liverworts  and  mosses)  the  thallus  is  still  present,  but 
there  is  added  the  highly  organized  archegonium  in  place  of  the  simple 
female  gamete  or  oogonium,  or  carpogonium  of  the  algae  and  fungi,  and  the 
sporophyte  has  become  a  distinct  though  still  dependent  structure.     In  the 
Pteridophytes  the  thallus  is  still  present  as  the  prothallium,  archegoina  are 
also  present,  and  while  both  of  these  structures  are  retrograding  the  spo- 
rophyte has  become  independent  and  has  organized  for  the  first  time  a  true 


338  MORPHOLOG  Y. 

vascular  system  for  conduction  of  water  and  food.  In  the  gymnosperms 
and  angiosperms  the  thallus  is  present  in  the  endosperm;  distinct,  though 
reduced,  archegonia  are  present  in  most  gymnosperms  and  represented 
only  by  the  egg  in  the  angiosperms;  the  vascular  system  is  still  more  highly 
developed  while  the  seed  for  the  first  time  is  organized,  and  characterizes 
these  plants  so  that  they  are  called  seed  plants,  or  Spermatophytes. 

Variation,  Hybridization,  Mutation. 

674a.  Variation. — It  is  a  well-known  fact  that  plants  as  well  as  ani- 
mals are  subject  to  variation.  Under  certain  conditions,  some  of  which 
are  partly  understood  and  others  are  unknown,  the  progeny  of  plants  dif- 
fer in  one  or  more  characters  from  their  parents.  Some  of  these  variations 
are  believed  to  be  due  to  the  influence  of  environment  (see  Parts  III  and 
IV).  Others  are  the  result  of  the  crossing  of  individuals  which  show 
greater  or  lesser  differences  in  one  or  more  characters,  or  the  crossing  of 
different  species  (hybridization").  The  most  profound  variations  are  those 
which  spring  suddenly  into  existence  (mutation). 

674b.  Hybridization. — Two  different  species  are  "crossed"  where  the 
egg-cell  of  one  species  is  fertilized  by  the  sperm  of  another  species.  The 
progeny  resulting  from  such  a  cross  is  a  hybrid.  Hybrids  sometimes  resem- 
ble one  parent,  sometimes  another,  sometimes  both.  Where  the  parents 
differ  only  in  respect  to  one  character  of  an  organ  or  structure,  there  is  a 
regular  law  in  respect  to  the  progeny  if  they  are  self-fertilized.  In  the 
first  generation  all  the  individuals  are  alike  and  resemble  one  of  the  parents, 
and  the  special  differential  character  of  that  parent  is  called  the  dominant 
character.  In  the  second  generation  75%  possess  the  dominant  character, 
while  25%  resemble  the  other  original  parent,  and  its  differential  charac- 
ter is  called  recessive.  These  are  pure  recessives,  since  successive  genera- 
tions, if  self-fertilized,  are  always  recessive.  Of  the  75%  which  show  the 
dominant  character  in  the  second  generation,  one-third  (or  25%  of  the 
whole  number)  are  pure  dominants  if  self-fertilization  is  continued,  while 
50%  are  really  "cross  breds"  like  the  first  generation,  and  if  self -fertilized 
split  up  again  into  approximately  25  dominants,  50  cross  breds,  and  25 
recessives.  This  is  what  is  called  Mendel's  law.  Where  the  original  par- 
ents differ  in  respect  to  more  than  one  character,  the  result  is  more  compli- 
cated (see  Mendel's  Principles  of  Heredity;  also  de  Vries,  Das  Spaltungs- 
gesetz  der  Bastarde,  Per.  d.  deutsch.  bot.  Gesell.,  18,  83,  1900). 

674c.  Mutation. — This  term  is  applied  to  those  variations  which  appear 
so  suddenly  that  some  of  the  progeny  of  two  like  individuals  differ  from  all 
the  others  to  a  marked  degree.  Some  of  these  mutations  are  so  different 
as  to  be  regarded  as  new  species.  Some  of  the  primroses  show  mutations, 
and  (Enothera  gigas  is  a  mutation  from  (Enothera  lamarkiana  (see  de  Vries, 
Die  Mutationstheorie,  Leipzig) 


GAMETOPflYTE  AND    SPOROPHYTE. 


341 


the  nucleus,  giving  rise  to  a  succession  of  nuclear  figures  presented 
by  a  definite  but  variable  series  of  evolutions  on  the  part  of  the 
nuclear  substance.  This  is  indirect  division  of  the  nucleus,  or 
karyokinests.  Indirect  division  of  the  nucleus  is  the  usual  method, 
and  it  occurs  in  the  normal  growth  and  division  of  the  cell.  The 
nuclear  figures  which  are  formed  in  the  division  of  the  mother 
cell  into  the  four  spores  are  somewhat  different  from  those 
occurring  in  vegetative  division,  but  their  study  will  serve  to  show 
the  general  character  of  the  process. 

679.   Chromatin  and  linin  of  the  nucleus. — In  figure  404 
is  represented  a  pollen  mother  cell  of  the  May-apple  (podophyl- 


Fig.  404. 

Pollen  mother  cell 
of  podophyllum,  rest- 
ing nucleus.  Chroma- 
tin  forming  a  net- 
work. 

(Figures  404-406  after  Mottier.) 


Fig.  405. 

Spirem  stage  of  nucleus. 
nu,  nuclear  cavity ;  «,  nu- 
cleolus ;  S/>,  spirem. 


Fig.  406. 

Forming  spindle, 
threads  from  proto- 
plasm with  several 
poles,  roping  the 
chromosomes  up  to 
nuclear  plate. 


him).  The  nucleus  is  in  the  resting  stage.  There  is  a  network 
consisting  of  very  delicate  threads,  the  linin  network.  Upon 
this  network  are  numerous  small  granules,  and  at  the  junction  of 
the  threads  are  distinct  knots.  The  nucleolus  is  quite  large  and 
prominent.  The  numerous  small  granules  upon  the  linin  stain 
very  deeply  when  treated  with  certain  dyes  used  in  differentiating 
the  nuclear  structure.  This  deeply  staining  substance  is  the 
chromaiin  of  the  nucleus. 


342 


MORPHOLOG  Y. 


680.  The  chromatin  skein. — One  of  the  first  nuclear  figures 
in  the  preparatory  stages  of  division  is  the  chromatin  skein  or 
spirem.      The  chromatin    substance    unites  to  form    this.      The 
spirem  is  in  the  form  of  a  narrow  continuous  ribbon,  or  band, 
woven  into  an  irregular  skein,  or  gnarl,  as  shown  in  figure  405. 
This  band  splits  longitudinally  into  two  narrow  ones,  and  then 
each,  divides  into  a  definite  number  of  segments,  about  eight  in 
the  case  of  podophyllum.    Sometimes  the  longitudinal  splitting  of 
the  band  appears  to  take  place  after  the  separation  into  the  chro- 
matin segments.    The  segments  remain  in  pairs  until  they  separate 
at  the  nuclear  plate. 

681.  Chromosomes,  nuclear  plate,  and  nuclear  spindle. — 
Each  one  of  these  rod-like  chromatin  segments  is  a  chromosome. 


Karyokinesis  in  pollen  mother  cells  of  podophyllum.  At  the  left  the  spindle  with  the 
chromosomes  separating  at  the  nuclear  plate ;  in  the  middle  figure  the  chromosomes  have 
reached  the  poles  of  the  spindle,  and  at  the  right  the  chromosomes  are  forming  the  daughter 
nuclei.  (After  Mottier.) 

The  pairs  of  chromosomes  arrange  themselves  in  a  median  plane 
of  the  nucleus,  radiating  somewhat  in  a  stellate  fashion,  forming 
the  nuclear  plate,  or  monaster.  At  the  same  time  threads  of  the 
protoplasm  (kinoplasm)  become  arranged  in  the  form  of  a  spindle, 
the  axis  of  which  is  perpendicular  to  the  nuclear  plate  of  chromo- 
somes, as  shown  in  figure  407,  at  left.  Each  pair  of  chromosomes 
now  separate  in  the  line  of  the  division  of  the  original  spirem, 
one  chromosome  of  each  pair  going  to  one  pole  of  the  spindle, 


GAMETOPHYTE   AND    SPOROPHYTE. 


343 


Fig.  408. 

Different  stages  in  the  separation  of  divided 
U-shaped  chromosomes  at  the  nuclear  plate.  (After 
Mottier  )  In  podophyllum. 


while  the  other  chromosome  of  each  pair  goes  to  the  opposite 
pole.     The  chromosomes  here  unite  to  form  the  daughter  nuclei. 

Each  of  these  nuclei  now 
divide  as  shown  in  figure 
409  (whether  the  chromo- 
somes in  this  second  divi- 
sion in  the  mother  cell  split 
longitudinally  or  divide 
transversely  has  not  been 
definitely  settled),  and  four 
nuclei  are  formed  in  the 
pollen  mother  cell.  The 
protoplasm  about  each  one  of  these  four  nuclei  now  surrounds 
itself  with  a  wall  and  the  spores  are  formed. 

The  number  of  chromosomes  usually  the  same  in  a  given 
species  throughout  one  phase  of  the  plant. — In  those  plants 
which  have  been  carefully  studied,  the  number  of  chromosomes 
in  the  dividing  nucleus  has  been  found  to  be  fairly  constant  in  a 
given  species,  through  all  the  divisions  in  that  stage  or  phase 
of  the  plant,  especially  in  the  embryonic,  or  young  growing 
parts.  For  example,  in  the 
prothallium,  or  gameto- 
phyte,  of  certain  ferns,  as 
osmunda,  the  number  of 
chromosomes  in  the  divid- 
ing nucleus  is  always  twelve. 
So  in  the  development  of 
the  pollen  of  lilium  from 
the  mother  cells,  and  in  the 
divisions  of  the  antherid 
cell  to  form  the  generative 
cells  or  sperm  cells,  there 


Fig.  409. 
Second       division 


of 


twplvp    rhrnmn-  nuclei   in   pollen    mother    at 
twelve  D     cell     of  Fpodophyiium> 


Fig.  410. 

Chromosomes  uniting 
poles    to     form     the 
nuclei  of  the  four  spores. 
(After  Mottier.) 


SOmeS     SO     far    as    has    been  chromosomes  at  poes 

found.       In    the   development    of  the  egg  of  lilium  from  the 
macrospore  there  are  also  twelve  chromosomes. 


344 


MORPHOLOG  Y. 


When  fertilization  takes  place  the  number  of  chromosomes 
is  doubled  in  the  embryo. — In  the  spermatozoid  of  osmunda 
then,  as  well  as  in  the  egg,  since  these  are  developed  on  the  game- 
tophyte,  there  are  twelve  chromosomes  each.  The  same  is  true 
in  the  sperm-cell  (generative  cell)  of  lilium,  and  also  in  the  egg- 
cell.  When  these  nuclei  unite,  as  they  do  in  fertilization,  the 
paternal  nucleus  with  the  maternal  nucleus,  the  number  of  chro- 
mosomes in  the  fertilized  egg,  if  we  take  lilium  as  an  example, 
is  twenty-four  instead  of  twelve;  the  number  is  doubled.  The 
fertilized  egg  is  the  beginning  of  the  sporophyte,  as  we  have  seen. 
Curiously  throughout  all  the  divisions  of  the  nucleus  in  the  em- 
bryonic tissues  of  the  sporophyte,  so  far  as  has  been  determined, 
up  to  the  formation  of  the  mother  cells  of  the  spores,  the  number 
of  chromosomes  is  usually  the  same 

682.  Reduction  of  the  number  of  chromosomes  in  the  nu- 
cleus.— If  there  were  no  reduction  in  the  number  of  chromosomes 


Fig.  411. 

Karyokmesis  in  sporophyte  cells  of    podophyllum  (twice    the  number  of  chromosomes 
here  that  are  found  in  the  dividing  spore  mother  cells). 

at  any  point  in  the  life  cycle  of  plants,  the  number  would  thus 
become  infinitely  large.    A  reduction,  however,  does  take  place. 


GAMETOPHYTE  AND    SPOROPHYTE.  345 

This  usually  occurs,  either  in  the  mother  cell  of  the  spores  or  in 
the  divisions  of  its  nucleus,  at  the  time  the  spores  are  formed.  In 
the  mother  cells  a  sort  of  pseudo-reduction  is  effected  by  the 
chromatin  band  separating  into  one  half  the  usual  number  of  nu- 
clear segments.  So  that  in  lilium  during  the  first  division  of  the 
nucleus  of  the  mother  cell  the  chromatin  band  divides  into  twelve 
segments,  instead  of  twenty-four  as  it  has  done  throughout  the 
sporophyte  stage.  So  in  podophyllum  during  the  first  division  in 
the  mother  cell  it  separates  into  eight  instead  of  into  sixteen. 
Whether  a  qualitative  reduction  by  transverse  division  of  the 
spirem  band,  unaccompanied  by  a  longitudinal  splitting,  takes 
place  during  the  first  or  second  karyokinesis  is  still  in  doubt. 
Qualitative  reduction  does  take  place  in  some  plants  according 
to  Beliaieff  and  others.  Recently  the  author  has  found  that  it 
takes  place  in  Trillium  grandiflorum  during  the  second  karyoki- 
nesis, and  in  Arisaema  triphyllum  the  chromosomes  divide  both 
transversely  and  longitudinally  during  the  first  karyokinesis  form- 
ing four  chromosomes,  and  a  qualitative  reduction  takes  place  here. 

683.  Significance  of  karyokinesis  and  reduction. — Thepre 
cision  with  which  the  chromatin  substance  of  the  nucleus  is  di- 
vided, when  in  the  spirem  stage,  and  later  the  halves  of  the 
chromosomes  are  distributed  to  the  daughter  nuclei,  has  led  to  the 
belief  that  this  substance  bears  the  hereditary  qualities  of  the 
organism,  and  that  these  qualities  are  thus  transmitted  with  cer- 
tainty to  the  offspring.  In  reduction  not  only  is  the  original 
number  of  chromosomes  restored,  it  is  believed  by  some  that 
there  is  also  a  qualitative  reduction  of  the  chromatin,  i.e.  that 
each  of  the  four  spores  possesses  different  qualitative  elements  of 
the  chromatin  as  a  result  of  the  reducing  division  of  the  nucleus 
during  their  formation. 

The  increase  in  number  of  chromosomes  in  the  nucleus  occurs 
with  the  beginning  of  the  sporophyte,  and  the  numerical  reduc- 
tion occurs  at  the  beginning  of  the  gametophyte  stage.  The 
full  import  of  karyokinesis  and  reduction  is  perhaps  not  yet 
known,  but  there  is  little  doubt  that;  a  profound  significance  is  to 
be  attached  to  these  interesting  phenomena  in  plant  life. 


346 


MORPHOLOGY. 


684.  The  gametophyte  may  develop  directly  from  the  tissue 
of  the  sporophyte.  —If  portions  of  the  sporophyte  of  certain  of 
the   mosses,  as  sections  of  a  growing  seta,   or  of  the  growing 
capsule,  be  placed  on  a  moist  substratum,  under  favorable  condi- 
tions some  of  the  external  cells  will  grow  directly  into  protonemal 
threads.    In  some  of  the  ferns,  as  in  the  sensitive  fern  (onoclea), 
when  the  fertile  leaves  ^fe  expanding  into  the  sterile  ones,  proto- 
nemal   outgrowths  occur  among  the  aborted  sporangia  on  the 
leaves    of  the    sporophyte.      Similar    rudimentary    protonemal 
growths  sometimes  occur  on  the  leaves  of  the  common  brake 
(pteris)  among  the  sporangia,  and  some  of  the  rudimentary  spo- 
rangia become    changed  into  the  protonema.      In    some  other 
ferns,  as  in  asplenium(A.  filix-fcemina,  var.  clarissima),  prothallia 
are  borne  among  the  aborted  sporangia,  which  bear  antheridia 
and  archegonia.      In  these  cases  the  gametophyte  develops  from 
the  tissue  of  the  sporophyte  without  the  intervention  or  necessity 
of  the  spores.     This  is  apospory. 

685.  The  sporophyte  may  develop  directly  from  the  tissue 
of  the  gametophyte. — In  some  of  the  ferns,  Pteris  cretica  for 
example,  the  embryo  fern  sporophyte  arises  directly  from  the  tissue 
of  the  prothallium,  without 

the  intervention  of  sexual 
organs,  and  in  some  cases 
no  sexual  organs  are  de- 
veloped on  such  prothallia, 
Sexual  organs,  then,  and 
the  fusion  of  the  spermato- 
zoid  and  egg  nucleus  are 
not  here  necessary  for  the 
development  of  the  spo- 
rophyte. This  is  apogamy. 
Apogamy  occurs  in  some 
other  species  of  ferns,  and 
in  other  groups  of  plants  as  well,  though  it  is  in  general  a  rare 
occurrence  except  in  certain  species,  where  it  may  be  the  general 
rule. 


Fig.  412. 
Apogamy  in  Pteris  cretica. 


GAMETOPHYTE  AND   SPOROPHYTE.  347 

686.  Types  of  nuclear  division. — The  nuclear  figures  in  the 
vegetative  cells  are  usually  different  from  those  in  the  spore 
mother  cells.     In  the  spore  mother  cells  there  are  two  types  of 
nuclear  division,     (i)  The  first  division  in  the  mother  cell  is 
called    heterotypic.     The   early   stages   of   this   division   usually 
extend  over  a  longer  period  than  the  second,  and  the  figures  are 
more  complex.     Before  the  chromosomes  arrive  at  the  nuclear 
plate  they  are  often  in  the  form  of  rings,  or  tetrads,  or  in  the 
form  of  X,  V,  or  Y,  and  the  number  is  usually  one  half  the  num- 
ber in  the  preceding  cells  of  the  sporophyte.     (2)  The  homo- 
typic  division  immediately  follows  the  heterotypic  and  the  figures 
are  simpler,  often  the  chromosomes  being  of  a  hook  form,  or 
sometimes  much  stouter  than  in  the  heterotypic  division.     In 
the   vegetative   cells    (sometimes   called   somatic   cells,   or  body 
cells  in  contrast  with  reproductive  cells)  there  is  another  type, 
called  by  some  the  vegetative  type.     The  chromosomes  here  are 
often  in  the  form  of  the  letter  U,  and  the  figures  are  much  sim- 
pler than  in  the  heterotypic  division.     In  the  somatic  cells  of 
the  sporophyte,  as  stated  above,  the  number  of  chromosomes  is 
double  that  found  in  the  heterotypic  and  homotypic  divisions  of 
the  mother  cells  and  in  the  somatic  cells  of  the  gametophyte, 
Fig.  411  represents  a  late  stage  in  the  division  of  somatic  cells 
in  the  sporophyte  of  podophyllum.     The  root  tips  of  various 
plants  as  the  onion,  lily,  etc.,  are  excellent  places  in  which  to 
study  nuclear  division  in  the  somatic  cells  of  the  sporophyte. 

687.  Comparison  with  animals. — In  animals  there  does  not 
seem  to  be  anything  which  corresponds  with  the  gametophyte  of 
plants  unless  the  sperm  cells  and  eggs  themselves  represent  it. 
Heterotypic    and    homotypic    division    with    the    accompanying 
reduction  of  the  number  of  the  chromosomes  takes  place  in  ani- 
mals usually  in  the  mother  cells  of  the  sperms  and  eggs.     At 
the  time  of  fertilization  the  number  of  chromosomes  is  doubled, 
so  that  all  the  somatic  cells  (except  in  rare  instances)  from  the 
fertilized  egg  to  the  mother  cells  of  sperms  and  eggs  have  the 
doubled  number  of  chromosomes.     Reduction,  therefore,  takes 
place  in  animals  just  prior  to  the  formation  of  the  gametes,  while 


MORPHOLOGY. 

in  plants  it  takes  place  just  prior  to  the  formation  of  the  gameto* 
phytes. 

688.  Perhaps  there  is  not  a  fundamental  difference  between 
gametophyte  and  sporophyte. — This  development  of  sporophyte, 
or  leafy-stemmed  plant  of  the  fern  (parag.  685),  from  the  tissue 
of  the  gametophyte  is  taken  by  some  to  indicate  that  there  is  not 
such  a  great  difference  between  the  gametophyte  and  sporophyte 
of  plants  as  others  contend.  In  accordance  with  this  view  it  has 
been  suggested  that  the  leafy-stemmed  moss  plant,  as  well  as  the 
leafy  stem  of  the  liverworts,  is  homologous  with  the  sporophyte  or 
leafy  stem  of  the  fern  plant;  that  it  arises  by  budding  from  the 
protonema;  and  that  the  sexual  organs  are  borne  then  on  the 
sporophyte. 


PART  III. 

PLANT  MEMBERS  IN  RELATION  TO  ENVIRONMENT. 

CHAPTER  XXXVIII. 

THE   ORGANIZATION    OF   THE    PLANT. 
I.  Organization  of  Plant  Members.* 

689.  It  is  now  generally  conceded  that  the  earliest  plants  to 
appear  in  the  world  were  very  simple  in  form  and  structure. 
Perhaps,  the  earliest  were  mere  bits  of  naked  protoplasm,  not 


*  Suggestions  to  the  teacher. — In  the  study  of  the  flowering  plants  in  the 
secondary  school  and  in  elementary  courses  three  general  topics  are  suggested, 
ist,  the  study  of  the  form  and  members  of  the  plant  and  their  arrangement, 
as  in  Chapters  XXXVIII-XLV.  2d,  the  study  of  a  few  plants  repre- 
sentative of  the  more  important  families,  in  order  that  the  members  of  the 
plant,  as  studied  under  the  first  topic,  may  be  seen  in  correlation  with  the 
plant  as  a  whole  in  a  number  of  different  types;  also  to  be  able  to  recognize 
certain  family  likenesses  or  resemblances  (example,  to  recognize  plants  of  the 
lily  type,  the  ament  type,  the  mustard  type,  the  rose  type,  labiate  type,  com- 
posite type,  etc.),  as  in  Chapters  LVIII-LXV.  3d,  the  study  of  plants  in  their 
relation  to  environment,  as  in  Chapters  XLVI-LVII.  The  first  and 
second  topics  can  be  conducted  consecutively  in  the  class-room  and 
laboratory.  The  third  topic  can  be  studied  at  opportune  times  during  the 
progress  of  topics  i  and  2.  For  example,  while  studying  topic  i  excursions 
can  be  made  to  study  winter  conditions  of  buds,  shoots,  etc.,  if  in  winter 
period,  or  the  relations  of  leaves,  etc.,  to  environment,  if  in  the  growing 
period.  While  studying  topic  2  excursions  can  be  made  to  study  flower 
relations,  and  also  vegetation  relations  (formations,  etc.)  to  environment 
(see  Chapter  LVII).  It  is  believed  that  a  study  of  these  three  general 
topics  is  of  much  more  value  to  the  beginning  student  than  the  ordinary 
plant  analysis  and  determination  of  species. 

349 


35°  RELATION   TO   ENVIRONMENT. 

essentially  different  from  early  animal  life.  The  simplest  ones 
which  are  clearly  recognized  as  plants  are  found  among  the 
lower  algae  and  fungi.  These  are  single  cells  of  very  minute 
size,  roundish,  oval,  or  oblong,  existing  during  their  growing 
period  in  water  or  in  a  very  moist  substratum  or  atmosphere. 
Examples  are  found  in  the  red  snow  plant  (Spharella  nivalis), 
the  Pleurococcus,  the  bacteria;  and  among  small  colonies  of 
these  simple  organisms  (Pandorina)  or  the  thread-like  forms 
(Spirogyra,  (Edogonium,  etc.).  It  is  evident  that  some  of  the 
life  relations  of  such  very  simple  organisms  are  very  easily  ob- 
tained— that  is,  the  adjustment  to  environment  is  not  difficult. 
All  of  the  living  substance  is  very  closely  surrounded  by  food 
material  in  solution.  These  food  solutions  are  easily  absorbed. 
Because  of  the  minute  size  of  the  protoplasts  and  of  the  plant 
body,  they  do  not  have  to  solve  problems  of  transport  of  food  to 
distant  parts  of  the  body.  When  we  pass  to  more  bulky  organ- 
isms consisting  of  large  numbers  of  protoplasts  closely  com- 
pacted together,  the  problem  of  relation  to  environment  and  of 
food  transport  become  felt;  the  larger  the  organism  usually  the 
greater  are  these  problems.  A  point  is  soon  reached  at  which 
there  is  a  gain  by  a  differentiation  in  the  work  of  different  proto- 
plasts, some  for  absorption,  some  for  Conduction,  some  for  the 
light  relation,  some  for  reproduction,  and  so  on.  There  is  also 
a  gain  in  splitting  the  form  of  the  plant  body  up  into  parts  so  that 
a  larger  surface  is  exposed  to  environment  with  an  economy  in 
the  amount  of  building  material  required.  In  this  differentiation 
of  the  plant  body  into  parts,  there  are  two  general  problems  to 
be  solved,  and  the  plant  to  be  successful  in  its  struggle  for  exist- 
ence must  control  its  development  in  such  a  way  as  to  preserve 
the  balance  between  them,  (i)  A  ready  display  of  a  large  sur- 
face to  environment  for  the  purpose  of  acquiring  food  and  the 
disposition  of  waste.  (2)  The  protection  of  the  plant  from 
injuries  incident  to  an  austere  environment. 

It  is  evident  with  the  great  variety  of  conditions  met  with  in 
different  parts  of  the  same  locality  or  region,  and  in  different 
parts  of  the  globe,  that  the  plant  has  had  very  complex  problems 


ORGANIZATION  PLANT  MEMBERS.  35 1 

to  meet  and  in  the  solution  of  them  it  has  developed  into  a  great 
variety  of  forms.  It  is  also  likely  that  different  plants  would  in 
many  cases  meet  these  difficulties  in  different  ways,  sometimes 
with  equal  success,  at  other  times  with  varied  success.  Just  as 
different  persons,  given  some  one  piece  of  work  to  do,  are  likely 
to  employ  different  methods  and  reach  results  that  are  varied  as 
to  their  value.  While  we  cannot  attribute  consciousness  or 
choice  to  plants  in  the  sense  in  which  we  understand  these  qual- 
ities in  higher  animals,  still  there  is  something  in  their  "consti- 
tution" or  "character"  whereby  they  respond  in  a  different 
manner  to  the  same  influences  of  environment.  This  is,  per- 
haps, imperceptible  to  us  in  the  different  individuals  of  the  same 
species,  but  it  is  more  marked  in  different  species.  Because  of 
our  ignorance  of.  this  occult  power  in  the  plant,  we  often  speak  of 
it  as  an  "inherent"  quality. 

Perhaps  the  most  striking  examples  one  might  use  to  illustrate  the  dif- 
ferent line  of  organization  among  plants  in  two  regions  where  the  environ- 
ment is  very  different  are  to  be  found  in  the  adaptation  of  the  cactus  or 
the  yucca  to  desert  regions,  and  the  oak  or  the  cucurbits  to  the  land  condi- 
tions of  our  climate.  The  cactus  with  stem  and  leaf  function  combined  in 
a  massive  trunk,  or  the  yucca  with  bulky  leaves  expose  little  surface  in 
comparison  to  the  mass  of  substance,  to  the  dry  air.  They  have  tissue  for 
water  storage  and  through  their  thick  epidermis  dole  it  out  slowly  since 
there  is  but  little  water  to  obtain  from  dry  soil. 

The  cucurbits  and  the  oak  in  their  foliage  leaves  expose  a  very  large  sur- 
face in  proportion  to  the  mass  of  their  substance,  to  an  atmosphere  not  so 
severely  dry  as  that  of  the  desert,  while  the  roots  are  able  to  obtain  an 
abundant  supply  of  water  from  the  moist  soil.  The  cactus  and  the  yucca 
have  differentiated  their  parts  in  a  very  different  way  from  the  oak  or  the 
cucurbits,  in  order  to  adapt  themselves  to  the  peculiar  conditions  of  the 
environment. 

When  we  say  that  certain  plants  have  the  power  to  adapt  themselves  to 
certain  conditions  of  environment,  we  do  not  mean  to  say  that  if  the  cucur- 
bits were  transferred  to  the  desert  they  would  take  on  the  form  of  the  cactus 
or  the  yucca.  They  could  do  neither.  They  would  perish,  since  the  change 
would  be  too  great  for  their  organization.  Nor  do  we  mean,  that,  if  the 
cactus  or  yucca  were  transferred  from  the  desert  to  our  climate,  they  would 
change  into  forms  with  thin  foliage  leaves.  They  could  not.  The  fact  is 
that  they  are  enabled  to  live  in  our  climate  when  we  give  them  some  care, 
but  they  show  no  signs  of  assuming  characters  like  those  of  our  vegetation. 


RELATION   TO  ENVIRONMENT. 

What  we  do  mean  is,  that  where  the  change  is  not  too  great  nor  too  sudden, 
some  of  the  plants  become  slightly  modified.  This  would  indicate  that  the 
process  of  organization  and  change  of  form  is  a  very  slow  one,  and  is  there- 
fore a  question  of  time — ages  it  may  be — in  which  change  in  environment 
and  adaptation  in  form  and  structure  have  gone  on  slowly  hand  in  hand. 

690.  Members  of  the  plant  body.— The  different  parts  into 
which  the  plant  body  has  become  differentiated  are  from  one 
point  of  view,  spoken  of  as  members.  It  is  evident  that  the  sim- 
plest forms  of  life  spoken  of  above  do  not  have  members.  It  is 
only  when  differentiation  has  reached  the  stage  in  which  certain 
more  or  less  prominent  parts  perform  certain  functions  for  the 
plant  that  members  are  recognized.  In  the  algae  and  fungi 
there  is  no  differentiation  into  stem  and  leaf,  though  there  is  an 
approach  to  it  in  some  of  the  higher  forms.  Where  this  simple 
plant  body  is  flattened,  as  in  the  sea-wrack,  or  ulva,  it  is  a  jrond. 
The  Latin  word  for  frond  is  thallus,  and  this  name  is  applied  to 
the  plant  body  of  all  the  lower  plants,  the  algae  and  fungi.  The 
algae  and  fungi  together  are  sometimes  called  thallophytes,  or 
thallus  plants.  The  word  thallus  is  also  sometimes  applied  to 
the  flattened  body  of  the  liverworts.  In  the  foliose  liverworts 
and  mosses  there  is  an  axis  with  leaflike  expansions.  These 
are  believed  by  some  to  represent  true  stems  and  leaves;  by 
others  to  represent  a  flattened  thallus  in  which  the  margins  are 
deeply  and  regularly  divided,  or  in  which  the  expansion  has  only 
taken  place  at  regular  intervals. 

In  the  higher  plants  there  is  usually  great  differentiation  of 
the  plant  body,  though  in  many  forms,  as  in  the  duckweeds,  it  is 
in  the  form  of  a  frond.  While  there  is  a  great  variety  in  the 
form  and  function  of  the  members  of  the  plant  body,  they  are 
all  reducible  to  a  few  fundamental  members.  Some  reduce 
these  forms  to  three,  the  root,  stem,  lea);  while  others  to  two,  the 
root,  and  shoot,  which  is  perhaps  the  best  primary  subdivision, 
and  the  shoot  is  then  divided  into  stem  and  leaf,  the  leaf  being 
a  lateral  outgrowth  of  the  stem,  and  can  be  indicated  by  the  fol- 
lowing diagram: 


ORGANIZATION  PLANT  MEMBERS. 


353 


Plant  body 


c,  (  Stem. 

(  Shoot.  . .  \  T     r 

I  ( Leaf. 

'  Root. 


KINDS   OF  SHOOTS. 

691.  Since  it  is  desirable  to  consider  the  shoot  in  its  relation  to 
environment,  for  convenience  in  discussion  we  may  group  shoots 
into  four  prominent  kinds:    (i)  Foliage  shoots;    (2)  Shoots  with- 
out foliage  leaves;    (3)  Floral  shoots;     (4)  Winter  conditions  of 
shoots  and  buds.      Topic  (4)  will  be  treated  in  Chapter  XXXIX, 
section  IV. 

692.  (1st)  Foliage  shoots. — Foliage  shoots  are  either  aerial, 
when  their  relation  is  to  both  light  and  air;  or  they  are  aquatic, 
when  their  relation  is   to 

both  light  and  water.  They 
bear  green  leaves,  and 
whether  in  the  air  or  water 
we  see  that  light  is  one  of 
the  necessary  relations  for 
all.  Naturally  there  are 
several  ways  in  which  a 
shoot  may  display  its  leaves 
to  the  light  and  air  or 
water.  Because  of  the 
great  variety  of  conditions 
on  the  face  of  the  earth 
and  the  multitudinous 
kinds  of  plants,  there  is  the 


Fig.  413- 
Lupinus  perennis.     Foliage  shoot  and  floral 


shoot. 

greatest  diversity  presented 

in  the  method  of  meeting  these  conditions.  There  is  to  be  con- 
sidered the  problem  of  support  to  the  shoot  in  the  air,  or  in 
the  water.  The  methods  for  solving  this  problem  are  funda- 
mentally different  in  each  case,  because  of  the  difference  in  the 
density  of  air  and  water,  the  latter  being  able  to  buoy  up  the 
plant  to  a  great  degree,  particularly  when  the  shoot  is  provided 
with  air  in  its  intercellular  spaces  or  air  cavities.  In  the  solu- 


354  RELATION  TO  ENVIRONMENT. 

tion  of  the  problem  in  the  relation  of  the  shoot  to  aerial  en- 
vironment, stem  and  leaf  have  in  most  cases  cooperated;*  but 
in  view  of  the  great  variety  of  stems  and  their  modifications,  as 
well  as  of  leaves,  it  will  be  convenient  to  discuss  them  in  separate 
chapters. 

693.  (2d)  Shoots  without  foliage  leaves. — These  are  subter- 
ranean or  aerial.  Nearly  all  subterranean  shoots  have  also 
aerial  shoots,  the  latter  being  for  the  display  of  foliage  leaves 
(foliage  shoots),  and  also  for  the  display  of  flowers  (flower  shoots). 
The  subterranean  kinds  bear  scale  leaves,  i.e.,  the  leaves  not 
having  a  light  relation  are  reduced  in  size,  being  small,  and  they 
lack  chlorophyll.  Examples  are  found  in  Solomon's  seal,  man- 


Fig.  4130. 

Burrowing  type,  the  mandrake,  a  "rhizome." 

drake  (fig.  41 3 a),  etc.  Here  the  scale  leaves  are  on  the  bud  at 
the  end  of  the  underground  stem  from  which  the  foliage  shoot 
arises.  Aerial  shoots  which  lack  foliage  leaves  are  the  dodder, 
Indian  pipe-plant,  beech  drops,  etc.  These  plants  are  sapro- 
phytes or  parasites  (see  Chapter  IX).  Deriving  their  carbo- 
hydrate food  from  other  living  plants,  or  from  humus,  they  do 
not  need  green  leaves.  The  leaves  have,  therefore,  probably 
been  reduced  in  size  to  mere  scales,  and  accompanying  this 
there  has  been  a  loss  of  the  chlorophyll.  Other  interesting  ex- 
amples  of  aerial  shoots  without  foliage  leaves  are  the  cacti  where 


*  It  is  interesting  to  note  that  in  some  foliage  shoots  the  stem  is  entirely 
subterranean.  See  discussion  of  the  bracken  fern  and  sensitive  fern  in 
Chapter  XXXIX. 


ORGANIZATION:   PLANT  MEMBERS.  355 

the  stem  has  assumed  the  leaf  function  and  the  leaves  have 
become  reduced  to  mere  spines.  The  various  modifications 
which  shoots  have  undergone  accompanying  a  change  in  their 
leaf  relation  will  be  discussed  under  stems  in  Chapter  XXXIX. 

694.  (3d)  Floral  shoots.— The  floral  shoot  is  the  part  of  the 
plant  bearing  the  flower.  As  interpreted  here  it  may  consist  of 
but  a  single  flower  with  its  stalk,  as  in  Trillium,  mandrake,  etc., 
or  of  the  clusters  of  flowers  on  special  parts  of  the  stem,  termed 
flower  clusters,  as  the  catkin,  raceme,  spike,  umbel,  head,  etc.  In 
the  floral  shoot  as  thus  interpreted  there  are  several  peculiarities 
to  observe  which  distinguish  it  from  the  foliage  shoot  and  adapt" 
it  to  its  life  relations. 

The  floral  shoot  in  many  respects  is  comparable  to  the  foliage 
shoot,  as  seen  from  the  following  peculiarities: 

(1)  It  usually  possesses,  beside  the  flowers,  small  green  leaves 
which  are  in  fact  foliage  though  they  are  very  much  reduced  in 
size,  because  the  function  of  the  shoot  as  a  foliage  shoot  is  sub- 
ordinated to  the  function  of  the  floral  shoot.     These  small  leaves 
on  the  floral  shoot  are  termed  bracts. 

(2)  It  may  be  (a)  unbranched,  when  it  would  consist  of  a 
single  flower,  or  (b)  branched,  when  there  would  be  several  to 
many  flowers  in  the  flower  cluster. 

(3)  The  flower  bud  has  the  same  origin  on  the  shoot  as  the 
leaf  bud;  it  is  either  terminal  or  axillary,  or  both. 

(4)  The  members  of  the  flower  belong  to  the  leaf  series,  i.e., 
they  are  leaves,  but  usually  different  in  color  from  foliage  leaves, 
because  of  the  different  life  relation  which  they  have  to  perform. 
Evidence  of  this  is  seen  in  the  transition  of  sepals,  petals,  sta- 
mens, or  pistils,  to  foliage  leaves  in  many  flowers,  as  in  the  pond 
lily,  the  abnormal  forms  of  trillium,  and  many  monstrosities  in 
other  flowers  (see  Chapter  XXXIV). 

(5)  The  position  of  the  members  of  the  flower  on  its  axis, 
though  usually  more  crowded,  in  many  cases  follows  the  same 
plan  as  the  leaves  on  the  stem. 

The  various  kinds  of  floral  shoots  or  flower  clusters  will  be 
discussed  in  Chapter  XLII,  on  the  Floral  Shoot. 


RELATION  TO  ENVIRONMENT. 


II.  Organization  of  Plant  Tissues. 

695.  A  tissue  is  a  group  of  cells  of  the  same  kind  having  a 
similar  position  and  function.     In  large  and  bulky  plants  differ- 
ent kinds  of  tissue  are  necessary,  not  only  because  the  work  of 
the  plant  can  be  more  economically  performed  by  a  division  of 
labor,  but  also  cells  in  the  interior  of  the  mass  or  at  a  distance 
from  the  source  of  the  food  could  not  be  supplied  with  food  and 
air  unless  there  were  specialized  channels  for  conducting  food 
and  specialized  tissue  for  support  of  the  large  plant  body.    In 
these  two  ways  most  of  the  higher  plants  differ  from  the  simple 
ones.    The  tissues  for  conduction  are  sometimes  called  collec- 
tively the   mestome,   while   tissues  for  mechanical  support  are 
called  stereome.     Division  of  labor  has  gone  further  also  so  that 
there  are  special  tissues  for  absorption,  assimilation,  perception, 
reproduction,  and  the  like.    The  tissues  of  plants  are  usually 
grouped    into    three    systems:     (i)  The    Fundamental    System, 
(2)  The    Fibrovascular    System,    (3)  The    Epidermal    System. 
Some  of  the  principal  tissues  are  as  follows: 

1.  THE  FUNDAMENTAL  SYSTEM. 

696.  Parenchyma.  —  Tissue  composed  of  thin-walled  cells  which  in  the 
normal  state  are  living.     Parenchyma  forms  the  loose  and  spongy  tissue  in 
leaves,  as  well  as  the  palisade  tissue  (see  Chapter  IV)  ;  the  soft  tissue  in  the 
cortex  of  root  and  stem  (Fig.  414)^  as  well  as  that  of  the  pith,  of  the  pith 
rays  or  medullary  rays  of  the  stem;  and  is  mixed  in  with  the  other  elements 
of  the  vascular  bundle  where  it  is  spoken  of  as  wood  parenchyma  and  bast 
parenchyma;    and  it  also  includes  the  undifferentlated  tissue  (meristem)  in 
the  growing  tips  of  roots  and  shoots;    also  the  "intrafascicular"  cambium 
(i.e.,  between  the  bundles,   some  also  include  the  cambium  within  the 
bundle). 

697.  Collenchyma.  —  This  is  a  strengthening  tissue  often  found  in  the 
cortex  of  certain  shoots.     It  also  is  composed  of  living  cells.     The  cells 
are  thickened  at  the  angles,  as  in  the  tomato  and  many  other  herbs  (fig. 

414). 

698.  Sclerenchyma,  or  stone-tissue.  —  This  is  also  a  strengthening  tissue 
and  consists  of  cells  which  do  not  taper  at  the  ends  and  the  walls  are  evenly 
thickened,  sometimes  so  thick  that  the  inside  (lumen)  of  the  cell  has  nearly 
disappeared.     Usually  such  cells  contain  no  living  contents  at  maturity. 
Sclerenchyma  is  very  common  in  the  hard  parts  of  nuts,  and  underneath 


ORGANIZATION:   PLANT   TISSUES. 


357 


the  epidermis  of  stems  and  leaves  of  many  plants,  as  in  the  underground 
stems  of  the  bracken  fern,  the  leaves  of  pines  (fig.  415),  etc. 


Fig.  414.  Fig.  4iS. 

Transverse  section  of  portion  of  Margin  of  leaf  of  Firms  pinaster,  transverse 
tomato  stem.  ept  epidermis;  ch  section,  c,  cuticularized  layer  of  outer  wall 
chlorophyll-bearing  cells;  co,  collen-  of  epidermis;  i,  inner  non-cuticularized 
chyma;  cp,  parenchyma.  layer;  c',  thickened  outer  wall  of  marginal 

cell;  #,.*',  hypoderma  of  elongated  scle- 
renchyma,  p,  chlorophyll-bearing  paren- 
chyma; pr,  contracted  protoplasmic  con- 
tents. X8oo.  (After  Sachs.) 

699.  Cork. — In  many  cases  there  is  a  development  of  "cork"  tissue 
underneath  the  epidermis.  Cork  tissue  is  developed  by  repeated  division 
of  parenchyma  cells  in  such  a  way  that  rows  of  parallel  cells  are  formed 
toward  the  outside.  These  are  in  distinct  layers,  soon  lose  their  proto- 
plasm and  die;  there  are  no  intercellular  spaces  and  the  cells  are  usually 
of  regular  shape  and  fit  close  to  each  other.  In  some  plants  the  cell  walls 
are  thin  (cork  oak),  while  in 
others  they  are  thickened 
(beech).  The  tissue  giving 
rise  to  cork  is  called  "cork 
cambium,"  or  phellogen,  and 
may  occur  in  other  parts  of 
the  plant.  For  example, 
where  plants  are  wounded  the 
living  exposed  parenchyma 
cells  often  change  to  cork 
cambium  and  develop  a  pro- 
tective layer  of  cork.  The  Fig.  416. 

,        riii  •  Section  through  a  lenticel  of  Betula  alba  show. 

walls  oi   coik.  cells  contain  a  ing  stoma  at  top,  phellogen  below  producing  rows 
substance      termed      suberin,  of  flattened  cells,  the  cork.     (After  De  Bary.) 

which  renders  them  nearly  waterproof. 


358  RELATION  TO  ENVIRONMENT. 

700.  Lenticels. — These    are    developed    quite    abundantly    underneath 
stomates  on  the  twigs  of  birch,  cherry,  beech,  elder,  etc.     The  phellogen 
underneath  the  stoma  develops  a  cushion  of  cork  which  presses  outward 
in  the  form  of  an  elevation  at  the  summit  of  which  is  the  stoma  (fig.  416). 
The  lenticels  can  easily  be  seen. 

2.  THE   FIBROVASCULAR   SYSTEM. 

701.  Fibrous  tissue.* — This  consists  of  thick-walled  cells,  usually  with- 
out living  contents  which  are  elongated  and  taper  at  the  ends  so  that  the 
cells,  or  fibers,  overlap.     It  is  common  as  one  of  the  elements  of  the  vas- 
cular bundles,  as  wood  fibers  and  bast  fibers. 

702.  Vascular  tissue,  or  tracheary  tissue. — This  consists  of  the  vessels  or 
ducts,  and  tracheides,  which  are  so  characteristic  of  the  vascular  bundle 
(see  Chapter  V)  and  forms  a  conducting  tissue  for  the  flow  of  water.     The 
vascular  tissue  contains  spiral,  annular,  pitted,  and  scalariform  vessels  and 
tracheides  according  to  the  marking  on  the  walls  (figs.  58,  59).     These  are 
all  without  protoplasmic  contents  when  mature.     There  are  also  thin- 
walled  living  cells  intermingled  called  wood  parenchyma.     In  the  conifers 
(pines,  etc.)  the  tracheary  tissue  is  devoid  of  true  vessels  except  a  few  spiral 
vessels  in  the  young  stage,  while  it  is  characterized  by  tracheides  with  pecu- 
liar markings.     These  marks  on  the  tracheides  are  due  to  the  "bordered" 
pits  appearing  as  two  concentric  rings  one  within  the  other.     These  can  be 
easily  seen  in  a  longitudinal  section  of  wood  of  conifers. 

703.  Sieve  tissue. — This  consists  of  elongated  tubular  cells  connected  at 
the  ends,  the  cross  walls  being  perforated  at  the  ends.     These  are  in  the 
phloem  part  of  the  bundle,  and  serve  to  conduct  downwards  the  dissolved 
substances  elaborated  in  the  leaves. 

704.  Fascicular  cambium. — This  is  the  living,  cell -producing  tissue  in 
the  vascular  bundle,  which  in  the  open  bundle  adds  to  the  phloem  on  one 
side  and  the  xylem  on  the  other. 

3.  THE   EPIDERMAL   SYSTEM. 

705.  To  the  epidermal  system  belong  the  epidermis  and  the  various  out- 
growths of  its  cells  in  the  form  of  hairs,  or  trichomes,  as  well  as  the  guard 
cells  of  the  stomates,  and  probably  some  of  the  reproductive  organs. 

706.  The  epidermis. — The  epidermis  proper  consists  of  a  single  layer  of 
external   cells   originating  from   the   outer  layer  of   parenchyma   cells   at 
the   growing    apex    of  the  stem  or  root.      These   cells  undergo   various 
modifications    of    form.      In  many    cases    they   lose    their    protoplasmic 
contents.      In  many  cases  the  outer  wall   becomes   thickened,    especially 


*  Some  fibers  occur  also  very  frequently  in  the  Fundamental  System, 
forming  bundle-sheaths,  or  strands  of  mechanical  tissue  in  the  cortex. 


ORGANIZATION:  PLANT   TISSUES. 


359 


in  plants  growing  in  dry  situations  or  where  they  are  exposed  to  drying 
conditions.  The  epidermal  cells  generally  become  considerably  flattened, 
and  are  usually  covered  with  a  more  or  less  well  developed  water-proof 
cuticle,  a  continuous  layer  over  the  epidermis.  In  many  plants  the  cuticle 
is  covered  with  a  waxy  exudation  in  the  form  of  a  thin  layer,  or  of  rounded 
grains,  or  slender  rods,  or  grains  and  needles  in  several  layers.  These 
waxy  coverings  are  sometimes  spoken  of  as  "bloom"  on  leaves  and  fruit. 

707.  Trichomes. — Trichome  is  a  general  term  including  various  hair- 
like  outgrowths  from  the  epidermis,  as  well  as  scales,  prickles,  etc.     These 
include  root  hairs,   rhizoids,   simple  or  branched  hairs,   glandular  hairs, 
glandular   scales,   etc.     Glandular  hairs   are   found  on  many  plants,   as 
tomato,  verbena,  primula,  etc.;   glandular  scales  on  the  hop;   simple-celled 
hairs  on  the  evening  primrose,  cabbage,  etc.;    many -celled   hairs  on  the 
primrose,  pumpkin;    branched  hairs  on  the  shepherd's  purse,  mullein,  etc., 
stellate  hairs  on  some  oak  leaves. 

For  stomates  see  Chapter  IV. 

4.  ORIGIN   OF   THE    TISSUES. 

708.  Meristem  tissue. — The  various  tissues  consisting  of  cells  of  dissimi- 
lar form  are  derived  from  young  growing  tissue  known  as  meristem*    Meri- 
stem tissue  consists  of  cells  nearly  alike  in  form,  with  thin  cell  walls  and 
rich  in  protoplasm.     It  is  situated  at  the  growing  regions  of  the  plants. 
In  the  higher  plants  these  re- 
gions in  general  are  three  in 

number,  the  stem  and  root 
apex,  and  the  cambium  cyl- 
inder beneath  the  cortex. 
Tissues  produced  from  the 
stem  and  root  apex  are  called 
primary,  those  from  the  cam- 
bium secondary.  In  most 
cases  the  main  bulk  of  the 
plant  is  secondary  tissue,  ^ 

while  in  the  corn  plant  it  is  all  ''  L  & 

primary. 

709.  Origin  of  stem  tissues.      Section   through   ^J^' pomt   Of   stem.     d. 
— Tust    back    of    the    apical  dermatogen;      p,    plerome;    periblem     between. 

J  .  .  ,        .      ,.      ,  (After  De  Bary.) 

menstem    in    a    longitudinal 

section  of  a  growing  point  it  can  be  seen  that  the  cells  are  undergoing  a 
change  in  form,  and  here  are  organized  three  formative  regions.  The 
outer  layer  of  cells  is  called  dermatogen  (skin  producer),  because  later  it 
becomes  the  epidermis.  The  central  group  of  elongating  cells  is  the  plerome 
(to  fill).  This  later  develops  the  central  cylinder,  or  stele,  as  it  is  called 


RELATION   TO  ENVIRONMENT. 

(fig.  417).  Surrounding  the  plerome  and  filling  the  space  between  it  and 
the  dermatogen  is  the  third  formative  tissue  called  the  periblem,  which  later 
forms  the  cortex  (bark  or  rind),  and  consists  of  parenchyma,  collenchyma, 
sclerenchyma,  or  cork,  etc.,  as  the  case  may  be.  It  should  be  understood 
that  all  these  different  forms  and  kinds  of  cells  have  been  derived  from 
meristem  by  gradual  change.  In  the  mature  stems,  therefore,  there  are 
three  distinct  regions,  the  central  cylinder  or  stele,  the  cortex,  and  the 
epidermis. 

710.  Central  cylinder  or  stele. — As  the  central  cylinder  is  organized  from 
the  plerome  it  becomes  differentiated  into  the  vascular  bundles,  the  pith, 
the  pith  rays  (medullary  rays)  which  radiate  from  the  pith  in  the  center 
between  the  bundles  out  to  the  cortex,  and  the  pericycle,  a  layer  of  cells 
lying  between  the  central  cylinder  and  the  cortex.  The  bundles  then  are 
farther  organized  into  the  xylem  and  phloem  portions  with  their  different 
elements,  and  the  fascicular  cambium  (meristem)  separating  the  xylem 
and  phloem,  as  described  in  Chapter  V.  Such  a  bundle,  where  the  xylem 
and  phloem  portions  are  separated  by  the  cambium  is  called  an  open  bun- 


Fig.  418. 

Concentric  bundle  from  stem  of  Polypodium  yulgare.  Xylem  in  the  center, 
surrounded  by  phloem  and  this  by  the  endodermis.  (From  the  author's  Biology 
of  Ferns.) 

die  (as  in  fig.  58).  Where  the  phloem  and  xylem  lie  side  by  side  in  the  same 
radius  the  bundle  is  a  collateral  one.  Dicotyledons  and  conifers  are  char- 
acterized by  open  collateral  bundles.  This  is  why  trees  and  many  other 


ORGANIZATION:   PLANT   TISSUES.  36* 

perennial  plants  continue  to  grow  in  diameter  each  year.  The  cambium 
in  the  open  bundle  forms  new  tissue  each  spring  and  summer,  thus  adding 
to  the  phloem  on  the  outside  and  the  xylem  on  the  inside.  In  the  spring 
and  early  summer  the  large  vessels  in  the  xylem  predominate,  while  in 
late  summer  wood  fibers  and  small  vessels  predominate  and  this  part  of 
the  wood  is  firmer.  Since  the  vascular  bundles  in  the  stem  form  a  circle  in 
the  cylinder,  this  difference  in  the  size  of  the  spring  and  late  summer  wood 
produces  the  "annual"  rings,  so  evident  in  the  cross-section  of  a  tree  trunk. 
Branches  originate  at  the  surface  involving  epidermis,  cortex,  and  the 
bundles. 

In  monocotyledonous  plants  (corn,  palm,  etc.)  the  bundles  are  not  regu- 
larly arranged  to  form  a  hollow  cylinder,  but  are  irregularly  situated  through 
the  stele.  There  is  no  meristem,  or  cambium,  left  between  the  xylem  and 
phloem  portions  of  the  bundle  and  the  bundle  is  thus  dosed  (as  in  fig.  60), 
since  it  all  passes  over  into  permanent  tissue.  In  most  monocotyledons 
there  is,  therefore,  practically  no  annual  increase  in  diameter  of  the  stem. 

711.  Ferns.  —  In  the  ferns  and  most  of  the  Pteridophytes  an  apical  meri- 
stem tissue  is  wanting,  its  place  being  taken 
by  a  single  apical  cell  from  the  several 
sides  of  which  cells  are  successively  cut 
off,  though  Isoetes  and  many  species  of 
Lycopodium  have  an  apical  meristem 
group.  In  most  of  the  Pteridophytes  also 
the  bundles  are  concentric  instead  of  col- 
lateral.  Fig.  418  represents  one  of  the  -^^^^ 
bundles  from  the  stem  of  the  polypody 
fern.  The  xylem  is  in  the  center,  this  Fi«-  419. 

surrounded  by  the  phloem,  the  phloem  by 


the  phloem  sheath,  and   this   in  turn  by   sclerenchyma;      a,     thin  -  walled 
.....  .  sclerenchyma  ;  par,  parenchyma. 

the   endodermis,  giving    a  concentric   ar- 

rangement of  the  component  tissues.  A  cross-section  of  the  stem  (fig. 
419)  shows  two  large  areas  of  sclerenchyma,  which  gives  the  chief  mechan- 
ical support,  the  bundles  being  comparatively  weak. 

712.  Origin  of  root  tissues.  —  A  similar  apical  meristem  exists  in  roots, 
but  there  is  in  addition  a  fourth  region  of  formative  tissue  in  front  of  the 
meristem  called  calyptrogen  (fig.  420).  This  gives  rise  to  the  "root  cap" 
which  serves  to  protect  the  meristem.  The  vascular  cylinder  in  roots  is 
very  different  from  that  of  the  stem.  There  is  a  solid  central  cylinder  in 
which  the  groups  of  xylem  radiate  from  the  center  and  groups  of  phloem 
alternate  with  them  but  do  not  extend  so  near  the  center  (fig.  421).  As  the 
root  ages,  changes  take  place  which  obscure  this  arrangement  more  or 
less.  Branches  of  the  roots  arise  from  the  central  cylinder.  In  fern 
roots  the  apical  meristem  is  replaced  by  a  single  four-sided  (tetrahedral) 


RELATION   TO  ENVIRONMENT. 


apical  cell,  the  root  cap  being  cut  off  by  successive  divisions  of  the  outer 
face,  while  the  primary  root  tissues  are  derived  from  the  three  lateral 
faces. 


Fig.  420. 

Median  longitudinal  section  of  the 
apex  of  a  root  of  the  barley,  Hordeum 
vulgare.  k,  calyptrogen;  d,  dermat- 
ogen;  c,  its  thickened  wall;  pr,  peri- 
blem;  pi,  pleronie;  en,  endodermis; 
«',  intercellular  air-space  in  process  of 
formation;  a,  cell  row  destined  to  form 
a  vessel;  r,  exfoliated  cells  of  the  toot 
cap.  (After  Strasburger.) 


Fig.  421. 

Cross-section  of  fibrovasculay  bundle 
in  adventitious  root  of  Ranunculus  re- 
pens,  w,  pericycle ;  g,  four  radial  plates 
of  xylem;  alternating  with  them  are 
gioxips  of  phloem.  This  is  a  radial 
bundle.  (After  De  Bary.) 


Function  of  the  root  cap. — The  root  cap  serves  an  important  function  in 

protecting  the  delicate  meristem  or  cambium  at  the  tip  of  the  root.  These 
cells  are,  of  course,  very  thin-walled,  and  while  there  is  not  so  much  danger 
that  they  would  be  injured  from  dryness,  since  the  soil  is  usually  moist 
enough  to  prevent  evaporation,  they  would  be  liable  to  injury  from  friction 
with  the  rough  particles  of  soil.  No  similar  cap  is  developed  on  the  end 
of  the  stem,  but  ihe  meristem  here  is  protected  by  the  overlapping  bud- 
scales.  One  of  the  most  striking  illustrations  of  a  root  cap  may  be  seen  in 
the  case  of  the  Pandanus,  or  screw-pine,  often  grown  in  conservatories  (see 
fig.  447).  On  the  prop  roots  which  have  not  yet  reached  the  ground  the 
root  caps  can  readily  be  seen,  since  they  are  so  large  that  they  fit  over  the 
end  of  the  root  like  a  thimble  on  the  finger. 


ORGANIZATION:   PLANT  TISSUES. 


363 


713.  Descriptive  Classification  of  Tissues. 
Epidermis. 


Epidermal 
System. . 


Fibrovascular 
System 


Simple  hairs. 
Many-celled  hairs. 
Branched  hairs,  often  stellatCo 
Trichomes.         -I   Clustered,  tufted  hairs. 
Glandular  hairs. 
Root  hairs. 
Prickles. 

Guard-cells  of  stomates. 

Spiral  vessels. 

Pitted  vessels 

Scalariform  vessels, 
Xylem  (wood),  -j  Annular  vessels. 

Tracheides. 

Wood  fibers. 

Wood  parenchyma. 
Cambium  (fascicular). 


Phloem  (bast). 


Fundamental 
System 


Stem  and  root.  • 


Sjeve  -tubes, 
feast  fibers. 
Companion  cells. 

;t  parenchyma. 
Cork. 

Collenchyma. 
Parenchyma. 
Fibers. 
Milk  tissue. 


Cortex. 


_..  .  (  Parenchvma. 

Pith-ray.,  j 


Pith... 


Intrafascicular  cambium 

Parenchyma. 
Sclerenchyma. 


Bundle-sheath. 
Endodermis. 


Leaves..         .  \  Palis^e  tissue. 

'   Spongy  parenchyma. 

Reproductive  Organs  (mainly  fundamental). 


3^4  RELATION  TO  ENVIRONMENT. 

714.  Physiological  Classification  of  Tissues. 

Formative  Tissue. 

Thin-walled  cells  composing  the  meristem,  capable  of  division  and  from 

which  other  tissues  are  formed. 
Protective  Tissue. 

Tegumentary  System. — Epidermis,  periderm,  bark  protecting  the  plant 
from  external  contact. 

Mechanical  System. — Bast  tissue,  bast-like  tissue,  collenchyma,  scler- 

enchyma,  afford  protection  against  harmful  bending,  pulling,  etc. 
Nutritive  Tissues. 

Absorptive  System. — Root  hairs  and  cells,  rhizoids,  aerial  root  tissue, 
.absorptive  leaf  glands,  absorptive  organs  in  seeds,  haustoria  of  para- 
sites, etc. 

Assimilatory  System. — Assimilating  cells  in  leaf  and  stem. 

Conductive  System. — Sieve  tissue,  tracheary  tissue,  milk  tissue,  conduct- 
ing parenchyma,  etc. 

Food-storing  System. — Water  reservoir,  water  tissue,  slime  tissue,  fleshy 
roots  and  stems,  endosperm  and  cotyledons,  etc. 

Aerating  System. — Air  spaces  and  tubes,  special  air  tissue,  air-seeking 
roots,  stomates,  lenticels,  etc. 

Secretory  and  Excretory  System. — Water  glands,  digestive  glands,  resin 

glands,  nectaries,  tannin,  pitch  and  oil  receptacles,  etc. 
Apparatus  and  Tissues  for  Special  Duties. 

Holdfasts. 

Tissues  of  movement,  parachute  hairs,  floating  tissue,  hygroscopic  tis* 
sue,  living  tissue. 

For  perceiving  stimuli. 

For  conducting  stimuli,  etc. 


CHAPTER  XXXIX. 

THE   DIFFERENT   TYPES   OF   STEMS.     WINTER 
SHOOTS  AND  BUDS. 

I.  Erect  Stems. 

715.  Columnar  type. — The  columnar  type  of  stem  may  be 
simple  or  branched.  When  branching  occurs  the  branches  are 
usually  small  and  in  general  subordinate  to  the  main  axis.  *  The 
sunflower  (Helianthus  annuus)  is  an  example.  The  foliage  part 
is  mainly  simple.  The  main  axis  remains  unbranched  during 
the  larger  part  of  the  growth  period.  The  principal  flowerhead 
terminates  the  stem.  Short  branches  bearing  small  heads  then 
arise  in  the  axils  of  a  few  of  the  upper  leaves.  In  dry,  poor  soil, 
or  where  other  conditions  are  unfavorable,  there  may  be  only 
the  single  terminal  flowerhead,  when  the  stem  is  unbranched. 
The  mullein  is  another  columnar  stem.  The  foliage  part  is 
rarely  branched,  though  branches  sometimes  occur  where  the 
main  axis  has  become  injured  or  broken.  The  flower  stem  is 
terminal.  The  corn  plant  and  the  Easter  lily  are  good  illustra- 
tions also  of  the  columnar  stem. 

Among  trees  the  Lombardy  poplar  (Populus  fastigiata)  is  at 
excellent  example  of  the  columnar  type.  Though  this  is  pro- 
fusely branched,  the  branches  are  quite  slender  and  small  in 
contrast  with  the  main  axis,  unless  by  some  injury  or  other  cause 
two  large  axes  may  be  developed.  As  the  technical  name  indi- 
cates, the  branching  is  fastigiate,  i.e.,  the  branches  are  crowded 
close  together  and  closely  surround  the  central  axis.  The  royal 
palm  and  some  of  the  tree  ferns  have  columnar,  simple  stems, 

365 


366 


RELATION   TO   ENVIRONMENT. 


but  the  large,  wide-spreading  leaves  at  the  top  of  the  stem  give 

the  plant  anything  but  a  cylin- 
drical habit.  Some  cedars  and 
arbor-vitae  are  also  columnar. 

The  advantages  of  the  colum- 
nar habit  of  stem  are  three:  (i) 
That  the  plant  stands  above 
other  neighboring  ones  of  equal 
foliage  area  and  thus  is  enabled 
to  obtain  a  more  favorable  light 
relation;  (2)  where  large  num- 
bers of  plants  of  the  same  species 
are  growing  close  together,  they 
can  maintain  practically  the 
same  habit  as  where  growing 
alone;  (3)  the  advantage  gained 
by  other  types  in  their  neighbor- 
hood in  less  shading  than  if  the 
type  Were  spreading.  The  cyl- 
indrical type  can,  therefore,  grow 
between  other  types  with  le^s 
competition  for  existence. 

716.  The  cone  type.— This  is 
well  exampled  in  the  larches, 
spruces,  the  gingko  tree,  some 
of  the  pines,  cedars,  and  other 
gymnosperms.  In  the  cone  type, 
the  main  axis  extends  through 
the  system  of  branches  like  a 
tall  shaft,  i.e.,  the  trunk  is  excur- 
rent.  The  lower  branches  are 
wide-spreading,  and  the  branches 
become  successively  shorter, 
usually  uniformly,  as  one  ascends 
the  stem.  The  branching  is  of 

two  types:  (i)  the  branches  are  in  false  whorls;  (2)  the  branches 


Fig.  422. 
Cylindrical  stem  of  mullein. 


TYPES  OF  STEMS. 


367 


are  distributed  along  the  stem.  To  the  first  type  belong  the 
pines,  Norway  spruce,  Douglas  pruce,  etc.  The  white  pine  is 
an  exquisite  example,  and  in 
young  and  middle-aged  trees 
shows  the  style  of  branching  to 
very  good  advantage.  The 
branches  are  nearly  horizontal, 
with  a  slight  sigmoid  graceful 
curve,  while  towards  the  top  the 
branches  are  ascending.  This 
direction  of  the  branches  is  due 
to  the  light  relation.  The  few 
whorls  at  the  top  are  ascending 
because  of  the  strong  light  from 
above.  They  soon  become  ex- 
tended in  a  horizontal  direction 
as  the  main  source  of  light  is 
shifting  to  the  side  by  the  shad- 
ing of  the  top.  The  ascending 
direction  first  taken  by  the  upper 
branches  and  their  subsequent  turning  downward,  while  the  ends 
often  still  have  a  slight  ascending  direction  gives  to  the  older 
branches  their  sigmoid  curve. 

The  young  vernal  shoots  of  the  pines  show  some  very  interest- 
ing growth-movements.  There  are  two  growth  periods:  (i)  the 
elongation  of  the  shoot,  and  (2)  the  elongation  of  the  leaves. 
The  elongation  of  the  shoot  takes  place  first  and  is  completed  in 
about  six  weeks  or  two  months'  time.  The  direction  of  the 
shoot  in  the  first  period  seems  to  be  entirely  influenced  by  geot- 
ropism.  It  grows  directly  upward  and  stands  up  as  a  very 
conspicuous  object  in  strong  contrast  with  the  dark  green  foliage 
of  the  more  or  less  horizontal  shoots.  When  the  second  period 
of  growth  takes  place,  and  the  leaves  elongate,  the  shoot  bends 
downward  and  outward  in  a  lateral  direction. 

The  rate  of  growth  of  the  pines  can  be  very  easily  observed 
since  each  whorl  of  branches  (between  the  whorls  of  long  shoots 


Fig.  423. 
Conical  type  of  larch. 


RELATION    TO   ENVIRONMENT. 

there  are  short  shoots  bearing  the  needle  leaves),  whether  on 
the  main  axis  or  on  the  lateral  branches,  marks  a  year,  the  new 
branches  arising  each  year  at  the  end  of  the  shoot  of  the  previous 
year.  The  rate  of  growth  is  sometimes  as  high  as  twelve  to 
twenty-four  inches  or  more  per  year. 

The  spruces  form  a  more  perfect  cone  than  the  pines.  The 
long  branches  are  mostly  in  whorls,  but  often  there  are  interme- 
diate ones,  though  the  rate  of  growth  per  year  can  usually  be 
easily  determined.  In  the  hemlock  spruce,  the  branching  is 
distributed.  The  larch  has  a  similar  mode  of  branching,  but  it 
is  deciduous,  shedding  its  leaves  in  the  autumn,  and  it  has  a  tall, 
conical  form. 

It  would  seem  that  trees  of  the  cone  type  possessed  certain 
advantages  in  some  latitudes  or  elevations  over  other  trees, 
(i)  A  conical  tree,  like  the  spruces  and  larches  and  the  pines, 
and  hemlocks  also,  before  they  get  very  old,  meets  with  less  injury 
during  high  winds  than  trees  of  an  oval  or  spreading  type.  The 
slender  top  of  the  tree  where  the  force  of  the  wind  is  greatest 
presents  a  small  area  to  the  wind,  while  the  trunk  and  short 
slender  branches  yield  without  breaking.  Perhaps  this  is 
one  reason  why  trees  of  this  type  exist  in  more  northern  latitudes 
and  at  higher  elevations  in  mountainous  regions,  and  why  the 
spruce  type  reaches  a  higher  latitude  and  altitude  even  than  the 
pines.  (2)  The  form  of  the  tree  is  such  as  to  admit  light  to  a 
large  foliage  area,  even  where  the  trees  are  growing  near  each 
other.  The  evergreen  foliage,  persistent  for  several  years,  on 
the  wide-spreading  lower  branches,  probably  affords  some  pro- 
tection to  the  trees  since  this  cover  would  aid  in  maintaining  a 
more  equable  temperature  in  the  forest  cover  than  if  the  trees 
were  bare  during  the  winter.  (3)  There  is  less  danger  of  injury 
from  the  weight  of  snow  since  the  greater  load  of  snow  would  lie 
on  the  lower  branches.  The  form  of  the  branches  also,  espe- 
cially in  the  spruces,  permits  them  to  bend  downward  without 
injury,  and  if  necessary  unload  the  snow  if  the  load  becomes  too 
heavy. 

717.  The  oval  type.  -This  type  is  illustrated  by  the  oak,  chest- 


TYPES  OF  STEMS.  369 

nut,  apple,  etc.  The  trees  are  usually  deciduous,  i.e.,  cast  their 
leaves  with  the  approach  of  winter.  The  main  axis  is  some- 
times maintained,  but  more  often  disappears  (trunk  is  deliques- 
cent}, because  of  the  large  branches  which  maintain  an  ascending 
direction,  and  thus  lessen  the  importance  of  the  central  axis 
which  is  so  marked  in  the  cone  type.  Trees  of  this  type,  and  in 
fact  all  deciduous  trees,  exhibit  their  character  or  habit  to  better 
advantage  during  the  winter  season  when  they  are  bare.  Trees 
of  this  type  are  not  so  well  adapted  to  conditions  in  the  higher 
altitudes  and  latitudes  as  the  cone  type,  for  the  reason  given  in 
the  discussion  of  that  type.  The  deciduous  habit  of  the  oaks, 
etc.,  enables  them  to  withstand  heavy  winds  far  better  than  if 
they  retained  their  foliage  through  the  winter,  even  were  the 
foliage  of  the  needle  kind  and  adapted  to  endure  cold. 

718.  The  deliquescent  type. — The  elm  is  a  good  illustration 
of  this  type.     The  main  axes  and  the  branches  fork  by  a  false 
dichotomy,  so  that  a  trunk  is  not  developed  except  in  the  forest. 
The  branches  rise  at  a  narrow  angle,  and  high  above  diverge 
in  the  form  of  an  arch.     The  chief  foliage  development  is  lofty 
and  spreading. 

Trees  possess  several  advantages  over  vegetation  less  lofty. 
They  may  start  their  growth  later,  but  in  the  end  they  outgrow 
the  other  kinds,  shade  the  ground  and  drive  out  the  sun-loving 
kinds. 

II.  Creeping,  Climbing,  and  Floating  Stems. 

719.  Prostrate  type.— This  type  is  illustrated  by  creeping  or 
procumbent  stems,  as  the  strawberry,   certain  roses,   of  which 
a  good  type  is  one  of  the  Japanese  roses  (Rosa  wichuriana), 
which  creeps  very  close  to  the  ground,  some  of  the   raspberries, 
the  curcubits  like  the  squash,  pumpkin,   melons,   etc.     These 
often  cover  extensive  areas  by  branching  and  reaching  out  radi- 
ally on  the  ground  or  climbing  over  low  objects.     The  cucurbits 
should  perhaps  be  classed  with  the  climbers,  since  they  are  capa- 
ble of  climbing  where  there  are  objects  for  support,   but  they 
are  prostrate  when  grown  in  the  field  or  where  there  are  no  ob- 


370 


RELATION   TO   ENVIRONMENT. 


jects  high  enough  to  climb  upon.  In  the  prostrate  type,  there 
is  economy  in  stem  building.  The  plants  depend  on  the  ground 
for  support,  and  it  is  not  necessary  to  build  strong,  woody  trunks 
for  the  display  of  the  foliage  which  would  be  necessary  in  the 
case  of  an  erect  plant  with  a  foliage  area  as  great  as  some  of  the 


Fig.  424- 
Prostrate  type  of  the  water  fern  (marsilia). 

prostrate  stems.  This  gain  is  offset,  at  least  to  a  great  extent, 
by  the  loss  in  ability  to  display  a  great  amount  of  foliage,  which 
can  be  done  only  on  the  upper  side  of  the  stem. 

Other  advantages  gained  by  the  prostrate  stems  are  protec- 
tion from  wind,  from  cold  in  the  more  rigorous  climates,  and 
some  propagate  themselves  by  taking  root  here  and  there,  as  in 
certain  roses,  the  strawberry  plant,  etc.  Some  plants  have 
erect  stems,  and  then  send  out  runners  below  which  take  root 
and  aid  the  plant  in  spreading  and  multiplying  its  numbers. 

720.  The  decumbent  type. — In  this  type  the  stem  is  first  erect, 
but  later  bends  down  in  the  form  of  an  arch,  and  strikes  root 
where  the  tip  touches  the  ground.  Some  of  the  raspberries 
and  blackberries  are  of  this  type. 


TYPES   OF  STEMS,  371 

721.  The  climbing  type.— The  grapes,  clematis,  some  roses, 
the  ivies,  trumpet  creeper,   the  climbing  bittersweet,  etc.,  are 
climbing  stems.     Like  the  prostrate  type,  the  climbers  economize 
in  the  material  for  stem  building.     They  climb   over  shrubs, 
up  the  trunks  of  trees  and  often  reach  to  a  great  height  and 
acquire  the  power  of  displaying  a  great  amount  of  foliage  by 
sending  branches  out  on  the  limbs  of  the  trees,  sometimes  devel- 
oping an  amount  of  foliage  sufficient  to  cover  and  nearly  smother 
the  foliage  of  large  trees;   while  the  main  stem  of  the  vine  may 
be  not  over  two  inches  in  diameter  and  the  trunk  of  the  supporting 
tree  may  be  three  feet  in  diameter. 

722.  Floating  stems. — These  are  necessarily  found  in  aquatic 
plants.     The    stems    may    be    ascending    or    horizontal.     The 
stems  are  usually  not  very  large,  nor  very  strong,  since  the  water 
bears  them  up.     The  plants  may  grow  in  shallow  water,  or  in 
water  10-12  feet  or  more  deep,  but  the  leaves  are  usually  formed 
at  or  near  the  surface  of  the  water  in  order  to  bring  them  near 
the  light.     Various  species  of  Potamogeton,  Myriophyllum,  and 
other  plants  common  along  the  shores  of  lakes,  in  ponds,  slug- 
gish streams,  etc.,  are  examples.     Among   the  algae  are  exam- 
ples like  Chara,  Nitella,  etc.,  in  fresh  water;   Sargassum,  Macro- 
cystis,  etc.,  in  the  ocean.     In  these  plants,  however,  the  plant 
body  is  a  thallus,  which  is  divided  into  stem-like  (caulidium)  and 
leaf-like  (phyllidium)  structures. 

723.  The  burrowing  type,  or  rhizomes. — These  are  horizon- 
tal, subterranean  stems.     The  bracken  fern,  sensitive  fern,  the 
mandrake  (see  fig.  4130),  Solomon's  seal,  Trillium,   Dentaria, 
and   the   like,   are   examples.     The   subterranean   habit   affords 
them  protection  from  the  cold,  the  wind,  and  from  injury  by 
certain  animals.     Many  of  these  stems  act  as  reservoirs  for  the 
storage  of  food  material  to  be  used  in  the  rapid  growth  of  the 
short-lived  aerial  shoot.     In  the  ferns  mentioned,  the  subterra- 
nean is  the  only  shoot,  and  this  bears  scale  leaves  which  are 
devoid  of  chlorophyll,  and  foliage  leaves  which  are  larger,  and 
the  only 'member  of  the  plant  body  which  is  aerial.     The  foliage 
leaf  has  assumed  the  function  of  the  aerial  shoot.     The  latter  i? 


372 


RELATION   TO  ENVIRONMENT. 


not  necessary  since  flowers  are  not  formed.  The  mandrake, 
Solomon's  seal,  Trillium,  etc.,  have  scale  leaves  on  the  fleshy 
underground  stems,  while  foliage  leaves  are  formed  on  the  aerial 
stems,  the  latter  also  bearing  the  flowers.  Some  of  the  advan- 
tages of  the  rhizomes  are  protection  from  injury,  food  storage 
for  the  rapid  development  of  the  aerial  shoot,  and  propagation. 

Many  of  the  grasses  have  subterranean  stems  which  ramify 
for  great  distances  and  form  a  dense  turf.  For  the  display  of 
foliage  and  for  flower  and  seed  production,  aerial  shoots  are 
developed  from  these  lateral  upright  branches. 

III.  Specialized  Shoots  and  Shoots  for  Storage  of 
Food.* 

724.  The  bulb.— The  bulb  is  in  the  form  of  a  bud,  but  the 
scale  leaves  are  large,  thick,  and  fleshy,  and  contain  stored  in 

them  food  products  manu- 
factured in  the  green  aerial 
leaves  and  transported  to  the 
underground  bases  of  the 
leaves.  Or  when  the  bulb  is 
aerial  in  its  formation,  it  is 
developed  as  a  short  branch  of 
the  aerial  stem  from  which 
the  reserve  food  material  is 
transported.  Examples  are 
found  in  many  lilies,  as  Easter 
Fig.  425.  lily,  Chinese  lilies,  onion,  tulip, 

Bulb  of  hyacinth.  ^      The  ^^  ^^  ^^  ^ 

closely  overlapped  and  surround  the  short  stem  within  (also 
called  a  tunicated  stem).  In  many  lilies  there  is  a  sufficient 


*  Besides  these  specialized  shoots  for  the  storage  of  food,  food-substances 
are  stored  in  ordinary  shoots.  For  example,  in  the  trunks  of  many  trees 
starch  is  stored.  With  the  approach  of  cold  weather  the  starch  is  con- 
verted into  oil,  in  the  spring  it  is  converted  into  starch  again,  and  later  as  the 
buds  begin  to  grow  the  starch  is  converted  into  glucose  to  be  used  for  food 
In  many  other  trees,  on  the  other  hand,  the  starch  changes  to  sugar  on  the 
approach  of  winter. 


TYPES  OF  STEMS. 


373 


amount  of  food  to  supply  the  aerial  stem  for  the  development 
of  flower  and  seed.  There  are  roots,  however,  from  the  bulb 
and  these  acquire  water  for  the  aerial  shoot,  and  when  planted 
in  soil  additional  food  is  obtained  by  them. 

725.  Corm. — A  corm  is  a  thick,   short,  fleshy,  underground 

stem.     A     good     example ^ 

is  found  in  the  jack-in-the- 

pulpit  (Arisaema). 

726.  Tubers.  — These 
are  thickened  portions  of 
the     subterranean     stems. 
The  most  generally  known 
example     is     the     potato 
tuber  (" Irish"  potato,  not 


the    sweet 
is  a  root). 


potato, 
The" 


which 


eyes 


of 


Fig.  426. 
Corm  of  Jack-in-the-pulpit. 


the  potato  are  buds  on  the 
stem  from  which  the  aerial 
shoots  arise  when  the  po- 
tato sprouts.  The  potato 
tuber  is  largely  composed 
of  starch  which  is  used  for 
food  by  the  young  sprouts. 

7260.  Phylloclades.  — 
These  are  trees,  shrubs,  or 
herbs  in  which  the  leaves  are  reduced  to  mere  bracts  and  stems, 
are  not  only  green  and  function  as  leaves,  but  some  or  all  of  the 
branches  are  flattened  and  resemble  leaves  in  form  as  in  Phyl- 
lanthus,  Ruscus,  Semele,  Asparagus,  etc.  The  flowers  are  borne 
directly  on  these  flattened  axes.  The  prickly  pear  cactus 
(Opuntia)  is  also  a  phylloclade.  Examples  of  phylloclades  are 
often  to  be  found  in  greenhouses. 

727.  Undifferentiated  stems  are  found  in  such  plants  as  the 
duckweed,  or  duckmeat  (Lemna,  Wolffia,  etc.    See  Chapter  III). 


374 


RELATION    TO  ENVIRONMENT. 


Fig.  427. 


twig 


IV.   Annual  Growth  and  Winter  Protec- 
tion of  Shoots  and  Buds.* 

728.  Winter   conditions,  f —  While   herbs  are 
subjected    only  to    the    damp   warm   atmosphere 
of  summer,  woody  plants    are  also  exposed  dur- 
ing the  cold  dry  winter,  and  must  protect  them- 
selves against  such  conditions.     The  air  is  dryer 
in  winter  than  in  summer;   while   at  the  same 
time  root  absorption   is  much    retarded   by   the 
cold   soil.      Then,   too,   the   osmotic    activity   of 
the  dormant  twig-cells  being  much  reduced,  the 
water-raising  forces   are  at  a  minimum.      It  is 
easy  to  see,  therefore,  that  a  tree  in  winter  is  prac- 
tically under  desert  conditions.     Moreover,  it  has 
been  found  by  various  investigators,  contrary  to 
the  general  belief,  that  cold  in  freezing  is  only  indi- 
rectly the  cause  of  death.     The  real  cause  is  the 
abstraction  of  water  from  the  cell  by  the  ice  crys^ 
tals  forming  in  the  intercellular  spaces.     Death 
ensues  because  the  water  content  is  reduced  below, 
the  danger-point  for  that  particular  cell.     It  was 
formerly  thought  that  on  freezing,  the  cells  in  the 
tissue  were  ruptured.     This  is  not  so.     Ice  almost 
never  forms  within  the  cell,  but  in  the  spaces 
between.     Freezing  then  is  really  a  drying  proc- 
ess, and  dryness,  not  cold,  causes  death  in  winter. 
To  protect  themselves  in  winter,   trees  provide 
various  waterproof  coverings  for  the  exposed  sur- 
faces and  reduce  the  activity  of  the  protoplasm 
so  that  it  will  be  less  easily  harmed  by  the  loss  of 
water  abstracted  by  the  freezing  process. 

729.  Protection  of  the  twig. — Woody  plants 
protect  the  living  cells  within  the  twigs  by  the 

*  production  of  a  dull  or  rough  corky  bark,  or  by  a 


of 

showing     buds     and 

leaf -scars.      (A   twig 

with  a  terminal  bud      *  This  topic  was  prepared  by  Dr.  K.  M.  Wiegand 

should  have  been  se-         ,   _         ..  ' 

lected  for  this  figure.)       f  See  discussion  of  Tropophytes  in  Chapter  XL VII. 


TYPES   OF  STEMS.  375 

thick  glossy  epidermis  over  the  entire  surface.  At  intervals 
occur  small  whitish  specks  called  lenticels,  which  here  perform 
nearly  the  same  function  as  do  stomates  in  the  leaf. 

730.  Bark  of  trunk. — A  similar  service  is  performed  by  the 
bark  for  the  main  trunk  and  branches  of  the  tree.     To  admit  of 
growth  in  diameter  the  old  bark  is  constantly  being  thrown  off 
in  strips,  flakes,  etc.,  and  replaced  by  a  new  but  larger  cylinder 
of  young  bark.     The  external  appearance  thus  produced  enables 
experienced  persons    to  recognize  many  kinds  of    trees  by  the 
trunk  alone. 

731.  Leaf-scars  and  bundle-scars. — The  presence  of  foliage 
leaves  during  the  winter  would  greatly  increase  the  transpiring 
surface  without  being  of  use  to  the  plant;  hence  they  are  usually 
thrown  off  'on  the  approach  of  winter.     The  scars  left  by  the 
fallen  leaves  are  termed  leaf-scars.     The  small  dots  on  the  leaf- 
scars  left  by  the  vascular  bundles  which  extended  through  the 
petiole    into    the    twig    are    termed    bundle-scars.     Sometimes 
stipule-scars  are  left  on  each  side  of  the  leaf-scar  by  the  fallen 
stipules. 

732.  Nodes  and  internodes. — The  region  upon  a  stem  where 
a  leaf  is  borne  is  termed  a  node.     The  space  between  two  nodes 
is  an  internode. 

733.  Phyllotaxy. — Investigation  of  a  horse-chestnut  or  willow  twig  will 
show  that  the  leaf-scars  occupy  definite  positions  which  are  constant  for 
each  plant  but  different  for  the  two  species.       The   arrangement  of  the 
leaves  on  the  stem  in   any  plant   is   termed   phyllotaxy.      In    the  horse- 
chestnut  we  find  two  scars  placed  at  the  same  node,  but  on  opposite  sides 
of  the  stem.     Somewhat  higher  up  we  find  two  more  similarly  placed,  but 
in  a  position  perpendicular  to  that  of  the  first  pair.     Such  phyllotaxy  is 
termed  opposite.     If  in  any  plant  several  leaves  occur  at  a  node,  the  phyl- 
lotaxy is  whorled.     If  but  one  at  each  node,  as  in  the  willow,  the  phyllotaxy 
is  alternate.      The  opposite  and   alternate   types   are  very  commonly  met 
with.     Closer  observation  will  show  that  in  the  willow,  if  a  line  be  drawn 
connecting  the  successive  leaf-scars,  it  will  pass  spirally  up  the  twig  until 
at  length  a  scar  is  reached  directly  over  the  one  taken  as  a  starting-point. 
Such  spiral  arrangement  always   accompanies  alternate  phyllotaxy.     The 
section  of  the   spiral  thus  delineated   is  termed  a  cycle.     We  express  the 
nature   of   the   cycle   by  the   fractions  £,  £,  f,  f,  j6^,   etc.,  in  which   the 


376 


RELATION   TO  ENVIRONMENT. 


Fig.  428.  Fig.  429. 

Fig.  428. — Shoot  of  butternut 
showing  leaf -scars,  axillary  buds, 
and  adventitious  buds  (buds  com- 
from  above  the  axils). 


numerator  denotes  the  number  of  turns 
around  the  stem  in  each  cycle,  and  the 
denominator  the  number  of  leaf-scars  in 
the  same  distance.  In  a  general  way  we 
find  in  plants  only  such  arrangements  as 
are  represented  by  the  fractions  given 
above.  These  fractions  show  the  curious 
condition  that  the  numerator  and  de- 
nominator of  each  is  equal  to  the  sum 
of  the  numerator  or  denominator  of  the 
two  preceding  fractions.  Much  specula- 
tion has  been  indulged  in  regarding  the 
significance  of  these  definite  laws  of  leaf- 
arrangement.  In  part  they  may  be  due 
to  the  desire  that  each  leaf  receive  the 
maximum  amount  of  light.  Only  certain 
definite  geometrical  conditions  will  insure 
this.  More  likely  it  is  due  to  the  economy 
of  space  alotted  to  the  leaf-fundaments 
in  the  bud.  Here,  again,  geometrical 
laws  govern  this  economy.  The  phyllo- 
taxy  is  nearly  constant  for  a  given  species. 

734.  Buds. — The  growing  point 
of  the  stem  or  branch  together  with 
its  leaf  or   flower  fundaments   and 
protective    structures   is   termed   a 
bud.     Winter  buds  on  woody  plants 
are    terminal    when    inclosing    the 
growing  point  of  the  main  axis  of  the 
twig;  lateral  when  the  growing  point 
is   that  of   a  branch   of   the   main 
axis.     Lateral  buds  are  always  axil- 
lary, i.e.,  situated  on  the  upper  angle 
between  a  leaf  and  the  main  axis. 

735.  Buds  occupying  special  po- 
sitions.—  Several   species  of  trees 
and  shrubs  produce  more  than  one 
bud  in  each  leaf -axil.      The  addi- 
tional ones  are  termed  accessory  or 


ing  irorn  above  the  axils).  !**»«••*•  «^n^o  ai.\*   \,\,L  LLL\,\J.  cn^^oo^j. j   ^ 

wWtfoi?-~Shoot  and  bud  °f     supernumerary  buds.      These  may 


TYPES   OF  STEMS.  377 

be  lateral  to  one  another  or  they  may  be  superposed  as  in  the  wal- 
nut or  butternut.  In  such  cases  some  of  the  buds  usually  contain 
simply  floral  shoots  and  are  termed  flower-buds.  In  some  species 
buds  are  frequently  produced  on  the  side  of  the  branches  and 
trunk  at  some  distance  from  the  leaf-axils,  and  entirely  without 
regard  for  the  latter;  or  more  rarely  may  occur  upon  the  root. 
Such  buds  are  termed  adventitious,  and  are  the  source  of  tthe 
feathery  branchlets  upon  the  trunks  of  the  American  elm. 

736.  Branching  follows  the  phyllotaxy. — Since  the  lateral  or 
branch-producing  buds  are  always  located  in  the  axil  of  a  leaf, 
the  branches  necessarily  follow  the  same  arrangement  upon  the 
main  axis  as  do  the  leaves.     Since,  however,  many  of  the  axil- 
lary buds  fail  to  develop,  this  arrangement  may  be  more  or  less 
obscured. 

737.  Coverings  of  winter-buds. — These  are  of  two  sorts,  hair 
and  cork,  or  scales.     Buds  protected  simply  by  dense  hair  or 
sunk  in  the  cork  of  the  twig  are  termed  naked  buds,  and  are 
comparatively  rare.     Most   species  protect  their  buds  by  the 
addition  of  an  imbricated  covering  of  closely  appressed  scales, 
the  whole  frequently  being  rendered  still  more  water-proof  by 
the  excretion  of  resin  between  the  scales  or  over  the  whole  sur- 
face.    The  scales  when  studied  carefully  are  found  to  be  much 
reduced  leaves  or  parts  of  leaves.     In  some  cases  they  represent 
a  modified  whole  leaf,  when  they  are  said  to  be  laminar,  or  a 
leaf -petiole,  when  they  are  petiolar,  or  stipular,  when  they  are 
much-specialized  stipules  of  a  leaf  which  itself  is  usually  absent. 
The  latter  type  is  much  the  less  common.     The  form  of  the  bud, 
the  nature  and  form  of  the  scales,  when  combined  with  characters 
furnished  by  the  leaf-  and  bundle-scars,   enable  one  to  recog- 
nize and  classify  the  winter  twigs  of  the  various  woody  species. 

738.  Phyllotaxy  of  the  bud-scales.— Since  the  bud-scales  are 
leaves,  they  follow  a  definite  phyllotaxy.     This  may  or  may  not 
be  the  same  as  that  of  the  foliage  leaves.     Twigs  with  opposite 
leaves  have  opposite  bud-scales,  or  if  with  alternate  leaves,  then 
alternate  bud-scales,  but  the  fractions  vary.     If  the  scales  are 
stipular,  then  there  are  of  course  two  at  each  node. 


378 


RELATION   TO  ENVIRONMENT. 


739.  Function  of  the  bud-coverings. — It  is  popularly  be- 
lieved that  the  scales  and  hairy  coverings  serve  to  keep  the  bud 
warm.  Research,  however,  shows  this 
to  be  almost  entirely  erroneous,  and 
that  the  thin  bud  coverings  are  en- 
tirely inadequate  to  keep  out  the  cold 
of  winter.  They  cannot  keep  the 
bud  even  a  degree  or  two  warmer  than 
the  outside  air,  except  when  the 
changes  are  very  rapid.  Experiment 
also  shows  that  the  modifying  effect 
of  the  covering  when  the  bud  thaws 
out  is  so  slight  as  to  be  almost  neg- 
ligible. Indeed,  a  thermometer  bulb 
covered  with  scales  taken  from  a 
horse-chestnut  bud  warmed  up  more 
rapidly  than  a  naked  one  when  ex- 
posed to  sunshine.  The  wool  in  the 
horse-chestnut  bud  is  not  for  the  pur- 
pose of  keeping  it  warm,  but  to  pro- 
tect the  young  shoot  from  too  great 
transpiration  after  the  bud  opens  the 
following  spring.  Research  has  also 
Bud  of  European  elm  in  sec-  shown  that  such  tempering  of  the 

tion,     showing     overlapping    of 

scales-  heat  conditions  is  not  especially  bene- 

ficial to  the  plant,  as  was  once  thought.  Neither  can  we  find  the 
main  function  in  the  prevention  of  water  from  entering  the  bud. 
This  might  be  accomplished  in  much  simpler  ways,  even  if  we 
could  demonstrate  the  desirability  of  keeping  the  water  out  at  all. 
The  true  functions  of  the  bud-scales  are  two  in  number: 
Firstly,  the  prevention  of  too  great  loss  of  water  from  the  young 
and  delicate  parts  within;  and  secondly,  the  protection  of  these 
same  parts  from  mechanical  injury.  Without  some  such  pro- 
tection the  delicate  young  structures  would  be  beaten  off  by  the 
wind,  or  become  the  food  for  hungry  birds  during  the  long  win- 
ter months. 


Fig.  430. 


TYPES   OF  STEMS. 


379 


740.  Opening  of  the  buds. — When  the  young  shoot  begins  to 
grow  in  the  spring,  the  bud-scales  are  forced  apart  or  open  of 
their  own  accord.  During  the  young  condition  the  shoot  is  very 
soft  and  brittle,  and  also  possesses  a  very  thin,  little  cutinized 
epidermis.  In  this  condition  it  is  especially  liable  to  mechanical 


Fig.  431. 
Opening  buds  of  hickory. 


injury  and  to  injury  from  drying  out.  We  find,  therefore,  a 
tendency  for  the  inner  bud-scales  to  elongate  during  vernation, 
thus  forming  a  tube  around  the  delicate  tissue  much  like  the 
opening  out  of  a  telescope.  The  young  leaves  and  internodes 


380  RELATION   TO  ENVIRONMENT. 

themselves  are  often  provided  with  a  woody  or  hairy  covering 
to  retard  transpiration.  When  the  epidermis  becomes  more 
efficient  the  hairy  covering  often  falls  away. 

In  the  case  of  naked  buds  protection  is  afforded  in  other  ways : 
by  the  protection  of  hairy  covering,  by  physiological  adaptation  of 
the  tissue,  or  in  many  cases  by  the  late  appearance  of  the  shoot 
in  spring  after  the  very  dry  April  and  May  winds  have  ceased. 

741.  Bud-scars,  and  how  to  tell  the  age  of  the  plant. — In  gen 
eral  the  bud-scales  when  they  fall  away  in  the  spring  leave  scars 
termed  scale-scars,  and  the  whole  aggregate  of  scale-scars  makes 
up  the  bud-scar.     The  position  of  the  buds  of  previous  winters  is, 
therefore,  marked.     It  becomes  an  easy  matter  to  determine  the 
age  of  a  branch,  since  all  that  is  necessary  is  to  follow  back  from 
one  bud-scar  to  another,  the  portion  of  the  stem  between  repre- 
senting, except  in  rare  cases,  one  year's  growth. 

A  woody  plant  grows  in  height  only  by  the  formation  of  new 
sections  of  stem  added  to  the  apex  or  side  of  similar  sections 
produced  the  previous  season,  never,  as  is  commonly  supposed, 
by  the  further  elongation  of  the  previous  year's  growth.  Hence  a 
branch  once  formed  upon  a  tree  is  fixed  as  regards  its  distance 
from  the  ground.  The  apparent  rise  of  the  branches  away  from 
the  ground  in  forest  trees  is  an  illusion  caused  by  the  dying  away 
of  the  lower  branches. 

742.  Definite  and  indefinite  growth.— With  the  opening  of 
the  buds  in  spring,  growth  begins.     In  some  cases,  when  all  the 
members  for  the  season  were  formed,  but  still  minute,  within  the 
bud,  such  growth  consists  solely  in  the  expansion  of  parts  already 
formed;   in  others  only  a  few  members  are  thus  present  to  ex- 
pand, while  new  ones  are  produced  by  the  growing  point  as  the 
season  progresses.     In  most  cases  growth  is  completed  by  the 
middle  of  July,  soon  after  which  buds  are  formed  for  next  year's 
growth.     Such  a  method  of  growth  is  termed  definite. 

In  a  few  woody  plants,  as,  for  example,  sumach,  locust,  and 
raspberry,  growth  continues  until  late  in  the  autunin.  In  such 
cases  the  most  recently  formed  nodes  and  internodes  are  unable 
to  become  sufficiently  "hardened"  before  winter  sets  in,  and 


TYPES  OF  STEMS. 


381 


are  killed  back  more  or  less.     Next  season's  shoot  is  a  branch 
from  some  axillary  bud.     Such  growth  is  termed  indefinite. 

743.  Structure  of  woody  stems. — If  we  make  a  cross-section  of  a  woody 
twig  three  general  regions  are  presented  to  view.  On  the  outside  is  the 
rather  soft,often  greenish  "  bark," 
so  called,  made  up  of  sieve  - 
tubes,  ordinary  parenchyma 
cells,  and  in  many  cases  long 
fibrous  cells  composing  the  "fi- 
brous bark."  From  a  growing 
layer  in  this  region,  termed  the 
phellogen,  the  true  corky  bark 
of  the  older  trunk  is  formed. 

Next  within  the  bark  we  find 
the  so-called  "woody"  portion 
of  the  twig.  This  is  strong  and 
resistant  to  both  breaking  and 
cutting.  The  microscope  shows 
it  to  be  composed  of  the  ordi- 
nary already  known  woody  ele- 
ments,*  wood-fibers,  for 
strengthening  purposes,  pitted 
and  spiral  vessels  as  conducting 
tissue ;  and  intermixed  with  these 
some  living  parenchyma  cells. 
A  cross-section  of  the  stem  also 
shows  narrow  radial  lines  through 
the  wood.  These  are  pith-rays, 
composed  of  vertical  plates  of 
living  parenchyma  cells.  These 
cells,  unlike  the  others  in  the 
wood,  are  elongated  radially, 
not  vertically.  The  height  of  the 
pith-rays  as  well  as  their  thick- 
ness varies  with  the  species  studied.  In  the  older  trunk  only  the  outer  por- 
tion, a  few  inches  in  thickness,  remains  light-colored  and  fresh,  and  is  called 
sap-wood.  The  inner  wood  is  usually  darker  and  harder,  and  is  termed 
heart-wood.  Living  parenchyma  cells,  in  general,  are  present  only  in  the 
sap-wood,  and  in  this  almost  solely  the  ascent  of  sap  occurs.  Dyestuffs 
and  other  substances  are  frequently  deposited  in  the  walls  of  the  heart-wood. 

The  third  region  occupying  the  center  of  the  twig  is  the  pith.      This 

*  Chapter  V,  and  Organization  of  Tissues  in  Chapter  XXXVIII. 


Fig.  432. 

Three-year-old  twig  of  the  American  ash, 
with  sections  of  each  year's  growth  showing 
annual  rings. 


382  RELATION   TO  ENVIRONMENT. 

is  composed  ordinarily  of  angular,  little  elongated,  parenchyma  cells, 
when  mature  mostly  without  cell-contents  and  filled  with  air.  The  pith 
region  in  different  trees  is  quite  diversified.  It  may  be  hollow,  chambered, 
contain  scattered  thick-walled  cells,  have  woody  partitions,  or  rarely  be 
entirely  thick- walled. 

The  nature  of  the  woody  ring  is  rather  perplexing  at  first;  but  its  origin 
is  simple.  We  may  conceive  that  it  has  developed  from  a  stem-type  like  the 
sunflower,  in  which  the  bundles,  though  separate,  are  connected  by  a  con- 
tinuous cambium  ring.  In  the  woody  twigs  the  numerous  bundles  are 
closely  packed  together,  and  only  separated  by  the  primary  pith-rays  ex- 
tending from  the  pith  to  the  cortex.  Other  secondary  pith-rays  are  pro- 
duced within  each  bundle,  but  they  usually  extend  only  part  way  from 
the  cortex  to  the  pith.  The  wood  represents  the  xylem  of  the  bundle, 
and  the  sieve-tubes  of  the  bark,  the  phloem. 

744.  Growth  in  thickness. — Although  the  year's  growth  does  not  in- 
crease in  length  after  the  first  season  has  passed,  it  does  increase  in  dianv 
eter  very  much.     From  the  size  of  an  ordinary  little  twig  it  may  at  length 
become  a  large  tree  trunk  several  feet  in  thickness.     Only  a  portion  of  the 
first  year's  growth  is  produced  by  the  growing  point.     All  the  rest  is  a 
product  of  the  cambium,  a  cylinder  of  wood  being  added  to  the  exterioi 
of  the  old  wood  each  season.     The  cambium,  here,  as  in  the  sunflower,  lies 
between  the  phloem  and  the  xylem,  forming  a  cylinder  entirely  around 
the  stem.     In  spring,  when  active,  it  becomes  soft  and  delicate,  thus  en 
abling  one  to  easily  strip  off  the  bark  from  some  trees,  such  as  willow,  etc., 
at  that  season. 

745.  Annual  rings  in  woody  stems. — The  wood  produced  by  the  cam. 
bium  each  season  is  not  homogeneous  throughout,  but  is  usually  much 
denser  toward  the  outer  part  of  the  yearly  cylinder,  wood-fibers  here  pre- 
dominating.    In   the  inner  portion   vessels   predominate,   giving   a  much 
more  porous  effect.     The  transition  from  one  year's  growth  to  another 
is  very  abrupt,  giving  rise  to  the  appearance  of  rings  in  cross- section.    Since 
ordinarily  in  temperate  climates  but  one  cylinder  of  wood  is  added  each 
year,  the  number  of  rings  will  indicate  the  age  of  the  trunk  or  branch. 
This  is  not  absolutely  accurate,  since  in  some  trees  under  certain  conditions 
more  than  one  ring  may  be  produced  in  a  summer.     The  porous  part 
of  the  ring  is  often  termed  "spring  wood,"  and  the  denser  portion  "fall 
wood,"  but  since  growth  from  the  cambium  ceases  in  most  trees  by  the 
middle  of  July,  "summer  wood"  would  be  more  appropriate  for  the  latter. 
It  is  mainly  the  alternation  of  the  cylinders  of  the  spring  and  summei 
wood  that   gives   the   characteristic   grain   to   lumber.     Pith-rays  play  an 
important  part  in  wood  graining  only  in  a  few  woods,  as,  for  instance,  in 
quartered  oak.     The  reason  for  the  production  of  porous  spring  wood 
and  dense  summer  wood  is  still  one  of  the  unsolved  problems  of  botany. 


CHAPTER  XL. 

FOLIAGE    LEAVES. 

I.  General  Form  and  Arrangement  of  Leaves. 

746.  Influence  of  foliage  leaves  on  the  form  of  the  stem. — 

The  marked  effect  which  foliage  has  upon  the  aspect  of  the  plant 
or  upon  the  landscape  is  evident  to  all  observers.  Perhaps  it  is 
usual  to  look  upon  the  stem  as  having  been  developed  for  the 
display  of  the  foliage  without  taking  into  account  the  possibility 
that  the  foliage  may  have  a  great  influence  upon  the  form  or 
habit  of  the  stem.  It  is  very  evident,  however,  that  the  foliage 
exercises  a  great  influence  on  the  form  of  the  stem.  For  ex- 
ample, as  trees  increase  in  age  and  size,  the  development  of 
branches  on  the  interior  ceases  and  some  of  those  already  formed 
die,  since  the  dense  foliage  on  the  periphery  of  the  trees  cuts 
off  the  necessary  light  stimulus.  The  tree,  therefore,  possesses 
fewer  branches  and  a  more  open  interior.  In  the  forest  also, 
the  dense  foliage  above  makes  possible  the  shapely,  clean  timber 
trunks.  Note  certain  trees  where  by  accident,  or  by  design,  the 
terminal  foliage-bearing  branches  have  been  removed  that  foliage- 
bearing  branches  may  arise  in  the  interior  of  the  tree  system. 

Without  foliage  leaves  the  stems  of  green  plants  would  develop 
a  very  different  habit  from  what  they  do.  This  development 
could  take  place  in  three  different  directions  under  the  influence 
of  light:  (i)  The  light  stimulus  would  induce  profuse  branch- 
ing, so  that  there  would  be  many  small  branches.  (2)  The  stem 
would  develop  fewer  branches,  but  they  would  be  flattened. 
(3)  Massive  trunks  with  but  few  or  no  branches.  In  fact,  all 

383 


384  RELATION   TO  ENVIRONMENT. 

these  forms  are  found  in  certain  green  stems  which  do  not  bear 
leaves.  An  example  of  the  first  is  found  in  asparagus  with  its 
numerous  crowded  slender  branches.  But  such  forms  in  our 
climate  are  rare,  since  foliage  leaves  are  more  efficient.  The 
second  and  third  forms  are  found  among  cacti,  which  usually 
grow  in  dry  regions  under  conditions  which  would  be  fatal  to 
ordinary  thin  foliage  leaves. 

747.  Relation  of  foliage  leaves  to  the  stem.— In  the  study  of 
the  position  of  the  leaves  on  the  stem  we  observe  two  important 
modes  of  distribution:    (i.)  the  distribution  along  the  individual 
stem  or  branch  which  bears  them,  usually  classed  under  the 
head  of  Phyllotaxy;   (2)  the  distribution  of  the  leaves  with  refer- 
ence to  the  plant  as  a  whole. 

748.  Phyllotaxy,  or  arrangement  of  leaves. — In  examining  buds  on  the 
winter  shoots  of  woody  plants,  we  cannot  fail  to  be  impressed  with  some 
peculiarities  in  the  arrangement  of  these  members  on  the  stem  of  the  plant. 

In  the  horse-chestnut,  as  we  have  already  observed,  the  leaves  are  in 
pairs,  each  one  of  the  pair  standing  opposite  its  partner,  while  the  pair 
just  below  or  above  stand  across  the  stem  at  right  angles  to  the  position  of 
the  former  pair.  In  other  cases  (the  common  bed-straw)  the  leaves  are 
in  whorls,  that  is,  several  stand  at  the  same  level  on  the  axis,  distributed 
around  the  stem.  By  far  the  larger  number  of  plants  have  their  leaves 
arranged  alternately.  A  simple  example  of  alternate  leaves  is  presented 
by  the  elm,  where  the  leaves  stand  successively  on  alternate  sides  of  the 
stem,  so  that  the  distance  from  one  leaf  to  the  next,  as  one  would  measure 
around  the  stem,  is  exactly  one  half  the  distance  around  the  stem.  This 
arrangement  is  one  half,  or  the  angle  of  divergence  of  one  leaf  from  the 
next  is  one  half.  In  the  case  of  the  sedges  the  angle  of  divergence  is  less, 
that  is  one  third. 

By  far  the  larger  number  of  those  plants  which  have  the  alternate  arrange- 
ment have  the  leaves  set  at  an  angle  of  divergence  represented  by  the  frac- 
tion two  fifths.  Other  angles  of  divergence  have  been  discovered,  and 
much  stress  has  been  laid  on  what  is  termed  a  law  in  the  growth  of  the 
stem  with  reference  to  the  position  which  the  leaves  occupy.  Singularly 
by  adding  together  the  numerators  and  denominators  of  the  last  two  fractions 
gives  the  next  higher  angle  of  divergence.  Example:  -  ~  =  |;  -  ,  |=~5 
and  so  on.  There  are,  however,  numerous  exceptions  to  this  regular 
arrangement,  which  have  caused  some  to  question  the  importance  of  any 
theory  like  that  of  the  "spiral  theory"  of  growth  propounded  by  Goethe 
and  others  of  his  time. 


FOLIAGE  LEAVES. 

749.  Adaptation  in  leaf  arrangement. — As  a  result,   however,   of  one 
arrangement  or  another  we  see  a  beautiful  adaptation  of  the  plant  parts 
to  environment,  or  the  influence  which  environment,  especially  light,  has 
had  on  the  arrangement  of  the  leaves  and  branches  of  the  plant.     Access 
to  light  and  air  are  of  the  greatest  importance  to  green  plants,  and  one 
cannot  fail  to  be  profoundly  impressed  with  the  workings  of  the  natural 
laws  in  obedience  to  which  the  great  variety  of  plants  have  worked  out 
this  adaptation  in  manifold  ways. 

750.  Distribution  of  leaves  with  reference  to  the  entire  plant. — In  this 
case,  as  in  the  former,  we  recognize  that  it  is  primarily  a  light  relation. 
As  the  plant  becomes  larger  and  more  branched  the  lower  and  inner  leaves 
disappear.     The  trees  and  shrubs  have  by  far  the  larger  number  of  leaves 
on  the  periphery  of  the  branch  system.     A  comparison  of  different  kinds 
of  trees  in  this  respect  shows,  however,  that  there  is  great  variation.    Trees 
with  dense  foliage  (elm,  Norway  maple,  etc.)   present  numerous   leaves 
on  the  periphery  which  admit  but  little  light  to  the  interior  where  leaves 
are  very  few  or  wanting.     The   sugar  maple  and  red  maple  do  not  cast 
such  a  dense  shade  and  there  are  more  leaves  in  the  interior.      This  is 
more  marked  in  the  silver  maple,  and  still  more  so  in  the  locust   (Gledit- 
schia  tricanthos). 

751.  Color  of  foliage  leaves. — The  great  majority  of  foliage  leaves  are 
green  in  color.     This  we  have  learned  (Chapter  VII)  is  due  to  the  presence 
of  a  green  pigment,  chlorophyll,  in  the  chloroplastids  thickly  scattered  in 
the  cells  of  the  leaf.     We  have  also  learned  that  in  the  great  majority  of 
cases,  the  light  stimulus  is  necessary  for  the  production  of  chlorophyll 
green.     There  are  many  foliage  leaves  which  possess  other  colors,  as  red 
(Rosa  rubrifolia),  purple  (the  purple  barberry,  hazel,  beech,  birch,  etc.), 
yellow  (the  golden  oak,  elder,  etc.);   while  many  others  have  more  or  less 
deep  tints  of  pink,  red,  purple,  yellow,  when  young.     All  of  these  leaves, 
however,  possess  chlorophyll  in  addition  to  red,  yellow,  purple  or  other 
pigment.     These  other  pigments  are  sometimes  developed  in  great  quan- 
tity in  the  cell-sap.     They  obscure  the  chlorophyll  from  view,  but  do  not 
interfere  seriously  with  the  action  of  light  and  the  function  of  chlorophyll, 
and  perhaps  in  some  cases  serve  as  a  screen  to  protect  the  protoplast. 

752.  Autumn  colors. — Foliage  leaves  of  many  trees  display  in  the  autumn 
gorgeous  colors.     These  colors  are  principally  shades  of  red  or  yellow, 
and  sometimes  purple.     The  autumn  color  is  more  marked  in  some  trees 
than  in  others.     In  the  red  maple,  the  red  and  scarlet  oak,  the  sourwood, 
etc.,   red  predominates,   though  sometimes  yellow  may  be  present  with 
the  red  in  a  single  leaf.     Sugar  maples,  poplars,  hickories,  etc.,  are  prin- 
cipally yellow  in  autumn.     The  sweet  gum  has  a  rich  variety  of  color-red, 
purple,  maroon,  yellow;  sometimes  all  these  colors  are  present  on  the  same 
tree 


386  RELATION  TO  ENVIRONMENT. 

The  red  and  purple  colors  are  found  suffused  in  the  cell-sap  of  certain 
cells  in  the  leaf  much  as  we  have  found  it  in  the  cells  of  the  red  beet.  The 
yellow  color  is  chiefly  due  to  the  disappearance  and  degeneration  of  the 
chlorophyll  while  the  leaf  is  in  a  moribund  state.  A  similar  phenomenon 
is  seen  in  the  yellowing  of  crops  when  the  soil  becomes  too  wet,  or  in  the 
blanching  of  grass  when  covered  with  a  board,  or  of  celery  as  the  earth 
is  ridged  up  over  the  leaves  in  late  summer  and  autumn.  A  number  of 
different  theories  have  been  advanced  to  explain  autumn  coloring,  i.e., 
the  appearance  of  the  red  coloring-matter.  It  has  been  attributed  to  the 
approach  of  cold  weather,  and  this  has  likely  led  to  the  erroneous  belief 
on  the  part  of  some  that  it  is  caused  by  frost.  It  very  often  precedes  frost. 
Some  have  attributed  it  to  the  action  of  the  more  oblique  light  rays  during 
autumn,  and  still  others  to  the  diminishing  water-supply  with  the  approach 
of  cool  weather.  The  question  is  one  which  has  not  met  as  yet  with  a 
satisfactory  solution,  and  is  certainly  a  very  obscure  one.  It  is  likely 
that  the  low  temperature  or  the  declining  activities  of  the  leaf  affect  certain 
organic  substances  in  the  leaf  and  give  rise  to  the  red  color,  and  it  is  quit* 
certain  that  in  some  years  the  display  is  more  brilliant  than  in  others. 
The  color  is  more  striking  in  some  regions  than  in  others  and  the  different 
soil,  as  well  as  climate,  has  been  supposed  to  have  some  influence.  The 
North  American  forests  are  noted  for  the  brilliant  display  of  autumnal 
color.  This  is  perhaps  due  to  some  extent  to  the  great  variety  or  number 
of  species  which  display  color.  It  would  seem  that  there  is  some  specific 
as  well  as  individual  peculiarities  in  certain  trees.  Some  individuals, 
for  example,  exhibit  brilliant  colors  every  autumn,  while  others  near  of 
the  same  species  are  more  subdued. 

It  has  been  shown  by  experiment  that  when  sunlight  passes  through 
red  colors  the  temperature  is  slightly  increased,  and  it  has  been  suggested 
that  this  may  be  of  protection  to  the  living  substance  which  has  ceased 
working  and  is  in  danger  of  injury  from  cold.  There  does  not  seem  to 
be  much  ground  for  this  suggestion,  however.  It  certainly  could  not 
protect  the  protoplasm  of  the  leaf  at  night  when  the  cold  is  more  intense, 
and  during  the  day  would  only  aggravate  matters  by  supplying  an  in- 
creased amount  of  heat,  since  extremes  of  heat  and  cold  in  alternation 
are  more  harmful  to  plant  life  than  uniform  cold.  Especially  would  this 
be  the  case  in  alpine  climates  where  the  alternation  of  heat  and  cold  be- 
tween  day  and  night  is  extreme,  and  brilliancy  of  the  colors  of  alpine  plants 
is  well  known.  It  seems  more  reasonable  to  suppose  that  the  red  color 
acts  as  a  screen,  as  the  chlorophyll  is  disappearing,  to  protect  from  the 
injurious  action  of  light,  certain  organic  substances  which  are  to  be  trans- 
ferred back  from  the  leaf  to  the  stem  for  winter  storage.  So  in  the  case 
ot  many  stems  in  the  spring  or  early  summer  when  the  young  leaves  often 
have  a  reddish  color,  it  is  likely  that  it  acts  as  a  screen  to  protect  the  living 


FOLIAGE   LEAVES.  387 

substance  from  the  strong  light  at  that  season  of  the  year  until  the  chloro- 
phyll screen,  which  is  weak  in  young  leaves,  becomes  darker  in  color  and 
more  effective,  when  the  red  color  often  disappears. 

753.  -  Function  of  foliage  leaves. — In  general  the  function  of 
the  foliage  leaf  as  an  organ  of  the  plant  is  fivefold  (see  Chapters 
IV,  VII,  VIII,  XI),  (i)  that  of  carbon-dioxide  assimilation  or 
photosynthesis,  (2)  that  of  transpiration,  (3)  that  of  the  synthesis 
of  other  organic  compounds,  (4)  that  of  respiration,  and  (5)  that 
of  assimilation  proper,  or  the  making  of  new  living  substance. 
While  none  of  these  functions  are  solely  carried  on  in  the  leaf, 
it  is  the  chief  seat  of  the  first  three  of  these  processes,  its  form, 
position,  and  structure  being  especially  adapted  to  the  purpose. 
Assimilation  proper,  as  well  as  respiration,  probably  take  place 
equally  in  all  growing  or  active  parts. 

754.  Parts  of  the  leaf.— All  foliage  leaves  possess  a  blade  or 
lamina,  so  called  because  of  its  expanded  and  thin  character. 
The  blade  is  the  essential  part.     Many  leaves,   however,   are 
provided  with  a  stalk  or  petiole  by  which  the  blade  is  held  out 
at  a  greater  or  lesser  distance  from  the  stem.     Leaves  with  no 
petiole  are  sessile,  the  blade  is  attached  by  one  end  directly  on 
the  stem.     In  some  cases  the  base  of  the  blade  is  wrapped  partly 
around  the  *stem,  or  in  others  it  extends  entirely  around  the 
stem  and  is  perjoliate.     Besides,  many  leaves  have  short  append- 
ages, termed  stipules,  attached  usually  on  opposite  sides  of  the 
petiole  at  its  junction  with  the  stem.     In  some  species  of  magnolia 
the  stipules  are  so  large  that  each  one  envelops  the  entire  portion 
of  the  bud  which  has  not  yet  opened.     Many  leaves  possess  out- 
growths in  the  form  of  hairs,  scales,  etc.     (See  leaf  protection.) 

755.  Simple  leaves. — Simple  leaves   are   those   in  which  the 
blade  is  plane  along  the  edge,  not  divided.     The  edge  may  be 
entire  or  indented  (serrate)  to  a  slight  extent  as  in  the  elm.     The 
form  of  the  simple  leaf  varies  greatly  but  is  usually  constant 
for  a  given  species,  or  it  may  vary  in  shape  in  the  same  species 
on  different  parts  of  the  plant.     Some  of  the  terms  applied  to 
the   outline   of   the   leaf   are   ovate,    oval,    elliptical,   lanceolate, 
linear,  needle-like,  etc.,  but  it  is  idle  for  one  to  waste  time  on 


388  RELATION-    TO   ENVIRONMENT. 

matters  of  minute  detail  in  form  until  it  becomes  necessary  for 
those  in  the  future  who  pursue  taxonomic  work.  It  is  evident 
that  a  simple  leaf,  except  those  of  minute  size,  possesses  advantages 
over  a  divided  leaf  in  the  amount  of  surface  it  exposes  to  the 
light.  But  in  other  respects  it  is  at  a  disadvantage,  especially 
as  it  increases  in  size,  since  it  casts  a  deeper  shade  and  does 
not  admit  of  such  a  free  circulation  of  air.  It  will  be  found, 
however,  in  our  study  of  the  relation  of  leaves  to  light  and  air 
that  the  balance  between  the  leaf  and  its  environment  is  ob- 
tained in  the  relation  of  the  leaves  to  each  other. 

756.  Venation  of  leaves. — A  very  prominent  character  of  the 
leaf  is  its  "venation. "  This  is  indicated  by  the  presence  of  numer- 
ous "  veins,"  indicated  usually  by  narrow  depressed  lines  on  the 
upper  surface,  and  by  more  or  less  distinct  elevated  lines  on  the 
under  surface.  There  are  two  general  types:  (i)  In  the  corn, 
Smilacina,  Solomon's  seal,  etc.,  the  veins  extend  lengthwise  of  the 
leaf  and  are  nearly  parallel.  Such  leaves  are  said  to  be  parallel- 
veined.  It  is  generally,  though  not  always,  a  character  of  mono- 
cotyledenous  plants.  (2)  In  the  elm,  rose,  hawthorn,  maple,  oak, 
etc.,  the  veins  are  not  all  parallel.  The  larger  ones  either  diverge 
from  the  base  of  the  blade  (palmate  leaf,  maple),  or  the  mid- 
vein  extends  through  the  middle  line  of  the  leaf,  while  other 
prominent  ones  branch  off  from  this  and  extend,  nearly  parallel, 
toward  the  edge  of  the  leaf  (pinnate  venation).  The  smaller 
intermediate  veins  which  are  also  very  distinct  extend  irregularly 
and  branch  and  anastomose  in  such  a  fashion  as  to  give  the  figure 
of  a  net  with  very  fine  meshes.  These  are  netted-veined  leaves. 
These  are  characteristic  of  most  of  the  dicotyledenous  plants. 
It  is  evident  from  what  has  been  said  of  the  examples  cited  that 
there  are  two  types  of  netted-veined  leaves,  the  palmate  and  pinnate. 

NOTE.  As  we  have  already  learned  in  Chapter  V  the  veins  contain  the 
vascular  bundles  of  the  leaf.  Through  them  the  water  and  food  solutions 
are  distributed  to  all  parts  of  the  leaf,  and  the  return  current  of  food  ma- 
terial elaborated  in  the  leaf  moves  back  through  the  bast  portion  into  the 
shoot.  The  veins  also  possess  a  small  amount  of  mechanical  tissue.  This 
forms  the  framework  of  the  leaf  and  aids  in  giving  rigidity  to  the  leaf  and 


FOLIAGE  LEAVES. 


.389 


in  holding  it  in  the  expanded  position.  The  mechanical  tissue  in  the 
framework  alone  could  not  support  the  leaf.  Turgescence  of  the  meso- 
phyll  is  needed  in  addition. 

757.  Cut  or  lobed  leaves. — In  many  leaves,  the  indentations 
on  the  margin  are  few  and 

deep.  Such  leaves  pre- 
sent several  lobes  the  pro- 
portionate size  of  which 
is  dependent  upon  the 
depth  of  the  indentation 
or  "incision."  Several 
of  the  maples,  oaks, 
birches,  the  poison  ivy, 
thistles,  the  dandelion, 
etc.,  have  lobed  leaves. 
Where  the  indentation 
reaches  to  or  very  near 
the  midrib  the  leaf  is 
said  to  be  cut.  A  study 
of  various  leaves  will 
show  all  gradations  from 
simple  leaves  with  plane  edges  to  those  which  are  cut  or  divided,  as 
in  compound  leaves,  and  the  lobes  are  often  variously  indented. 

758.  Divided,  or  compound  leaves. — The  rose,  sumac,  elder, 
hickory,  walnut,  locust,  pea,  clover,  American  creeper,  etc.,  are 
examples  of  divided  or  compound  leaves.     The  former  are  pin- 
nately  compound,  and  the  latter  are  palmately  compound.     The 
leaf  of  the  honey-locust  is  twice  pinnately  compound  or  bipin- 
nate,  and  some   are  three  times   pinnately  compound.*     It  is 

*  Some  of  the  different  terms  used  to  express  the  kinds  of  compound 
leaves  are  as  follows: 

Unifoliate  (for  a  single  leaflet,  as  in  orange  and  lemon  where  the  com- 
pound leaf  is  greatly  reduced  and  consists  of  one  pinna  attached  to  the 
petiole  by  a  joint).  Bifoliate  for  one  with  two  leaflets;  trifoliate  for  one 
with  three  leaflets,  as  in  the  clover;  plurifoliate  for  many  leaflets.  Odd 
pinnate  for  a  pinnate  leaf  with  one  or  more  pairs  of  leaflets  and  one  odd 
leaflet  at  the  end. 


Fig-  433- 
Lobed  leaves  of  oak  forming  a  mosaic. 


390 


RELATION    TO  ENVIRONMENT. 


evident  that  compound  leaves  are  only  extreme  forms  of  lobed 
or  cut  leaves  and  that  the  form  of  all  bears  a  definite  relation 
to  the  primary  venation.  There  has  been  a  reduction  of  meso- 
phyll  and  of  the  area  of  smaller  venation. 

759.  These  forms  of  leaves  probably  have  some  definite  sig- 
nificance. It  is  not  quite  clear  why  they  should  have  developed  as 

they  have;  though  it  is 
possible  to  explain  several 
important  relations  of  these 
forms  to  their  environ- 
ment, (i)  The  reduction 
of  the  surface  of  the  leaf, 
with  the  retention  of  the 
firmer  portions,  allows 
freer  movement  of  the  air 
and  affords  the  leaf  greater 
protection  from  injury  dur- 
ing violent  winds,  just  as 
the  finely  dissected  leaves 

tion  of  air  through  the' large 'leaf .  of        Some        Water  -  plants 

are  less  liable  to  injury  from  movement  of  the  more  dense 
medium  in  which  they  live.  It  is  possible  that  here  we  may 
have  an  explanation  of  one  of  the  factors  involved  in  this 
reduction  of  leaf  surface.  (2)  In  trees  with  compound  leaves, 
like  the  hickory,  walnut,  locust,  ailanthus,  etc.,  the  midvein, 
and  in  the  case  of  the  Kentucky  coffee-tree  (Gymnocladus)  the 
primary  lateral  veins  also,  serve  in  place  of  terminal  branches 
of  the  stem.  By  the  increase  in  the  outline  of  the  leaf  and 
the  reduction  of  its  surface  between  the  larger  veins,  the  tree 
has  attained  the  same  leaf  development  that  it  would  were  the 

So  leaves  are  palmately  bifoliate,  etc.,  pinnately  bifoliate,  etc.  Decom- 
pound leaves  are  those  where  they  are  more  than  twice  compound,  as 
ternately  decompound  in  the  common  meadow  rue  (Thalictrum). 

Perfoliate  leaves  are  seen  in  the  bellwort  (Uvularia),  connate  perfoliate, 
as  in  some  of  the  honeysuckles  where  the  bases  of  opposite  leaves  are  joined 
together  around  the  stem.  Equitant  leaves  are  found  in  the  iris,  where  the 
leaves  fit  over  one  another  at  the  base  like  a  saddle. 


Fig.  434- 

Twice    compound  leaf.     Leaflets   arranged   in 
one  plane,  but  open  spaces 


;rmit  free  circula- 


FOLIAGE  LEAVES.  391 

larger  veins  replaced  by  stems  bearing  simple  leaves.  The  tree 
as  it  is,  however,  has  the  advantage  of  being  able  to  cast  off  for 
the  winter  period  a  layer  of  what  otherwise  would  have  been  a 
portion  of  the  stem  system,  to  retain  which  through  the  winter 
would  use  more  energy  than  with  the  present  reduced  stem 
system,  and  the  stouter  stem  is  less  liable  to  dry  out.  In  the 
case  of  herbaceous  plants,  in  the  case  of  plants  like  most  of 
the  ferns  where  the  stem  is  on  the  underground  rootstock  (Pteris) , 
or  a  very  short  erect  stem,  as  in  the  Christmas  fern,  the  leaf 
replaces  the  aerial  stem,  and  the  division  (or  branching,  as  it  is 
sometimes  styled)  of  the  leaf  corresponds  to  the  branching  of  the 
stem.  This  is  more  marked  in  the  gigantic  exotics  like  Cibo- 
tium  regale,  and  in  the  tree  ferns  which  have  quite  tall  trunks, 
the  massive  compound  leaves  replace  branches.  In  the  palms 
and  cycads  are  similar  examples.  Those  who  choose  to  observe 
can  doubtless  find  many  examples  close  at  hand.  (3)  While 
divided  leaves  have  probably  not  been  evolved  in  response  to 
the  light  relation,  still  their  relation  in  this  respect  is  an  impor- 
tant one,  since  if  the  leaf  with  its  present  size  were  entire,  it 
would  cast  too  dense  a  shade  on  other  leaves  below. 

760.  General  structure  of  the  leaf. — The  general  structure  of  the  leaf 
has  been  already  studied  (see  Chapters  IV,  V,  VII).     It  is  only  necessary 
to  recall  the  main  points.     The  upper  and  lower  surfaces  of  the  leaf  are 
provided  with  a  layer  of  cells  usually  devoid  of  chlorophyll.     The  mesophyll 
of  the  leaf  consists  usually  of  a  layer  of  palisade  cells  beneath  the  epider- 
mis, and  the  remainder  consists  of  loose  parenchyma  with  large  intercel- 
lular spaces.     Through  the  mesophyll  course  the  "veins,"  or  fibro-vas- 
cular  strands,  consisting  of  the  xylem  and  phloem  portions  and  serving 
as  conduits  for  water,  salts,  and  foodstuffs.     In   the   epidermis   are   the 
stomata,  each  one  protected  by  the  two  guard  cells.     The  guard  cells  as 
well  as  the  mesophyll  contain  chlorophyll.     The  stomata  and  the  com- 
municating intercellular  spaces  furnish  the  avenues  for  the  ingress  and 
egress  of  gases,  and  for  the  escape  of  water  vapor. 

761.  Protection  of  leaves. — There  are  many  modifications  of  the  general 
plan  of  structure  in  different  leaves,  many  of  them  being  adaptations  for 
the   protection   of   the   leaf   under   adverse   or   trying   conditions.     Many 
leaves  are  also  capable  of  assuming  certain  positions  which  afford  them 
protection.     The  discussion  of  this  subject  may  be  presented  under  two 
general  heads:  Protective  modifications;    protective  positions. 


392  RELATION   TO  ENVIRONMENT. 

II.  Protective  Modification  of  Leaves. 

762.  General  directions  in  which  these  modifications  have 
taken  place. — The  usual  type  of  foliage  leaf  selected  is  that  of 
deciduous  trees  or  shrubs  or  of  our  common  herbs.     Such  a 
leaf  is  usually  greatly  expanded  and  thin  in  order  to  present  as 
great  a  surface  as  possible  in  comparison  with  its  mass,  since 
the  kind  of  work  which  the  leaf  has  to  do  can  be  more  effectu- 
ally carried  on  when  it  possesses  this  form.     This  form  of  leaf 
is  best  adapted  for  work  in  regions  where  there  is  a  medium 
amount  of  moisture  such  as  exists  in  the  temperate  zones.     But 
since  there  are  very  great  variations  in  the  climatic  and  soil 
conditions  of  these  regions,  and  even  greater  changes  in  desert 
and  arctic  regions,  the  type  of  leaf  described  is  unsuited  for 
all.     Its  own  life  would  be  endangered,  and  it  would  also  en- 
danger the  life  of  the  plant.     Modifications  have  therefore  taken 
place  to  meet  these  conditions,  or  at  least  those  plants  whose 
leaves   have   become   modified   in   those   directions   which    are 
suited  to  the  surrounding  conditions  have  been  able  to  persist, 
Excessive  cold  or  heat,  drought,  winds,  intense  light,  rain,  etc., 
are  some  of  the  conditions  which  endanger  leaves.     The  pro- 
tective modifications  of  leaves  may  be  grouped  under  four  gen- 
eral heads:     (i)   Structural  adaptations;    (2)   Protective  cover- 
ing; (3)  Reduction  of  surface;  (4)  Elimination  of  the  leaf  through 
the  complete  assumption  of  the  leaf  function  by  the  stem. 

763.  (i)  Structural  adaptations. — The  general  structure  of 
the  leaf  presents  certain  features  which  are  protective.     The  pali- 
sade layer  of  cells  found  usually  beneath  the  upper  epidermis 
forms  a  compact  layer  of  long  cells  which  not  only  acts  as  a 
light  screen  cutting  off  a  certain  amount  of  the  light,  since  too 
intense  light  would  be  harmful ;  it  also  aids  in  lessening  the  loss 
of  water  from  the  upper  surface,  where   radiation  is   greater. 
The  stomata  are  usually  on  the  under  side  of  aerial  leaves,  and 
the  mechanism  which  closes  them  when  the  leaf  is  losing  too 
much  water  is  protective.     As  a  protection  against  intense  light 
the  number  of  palisade  layers  is   sometimes  increased  or  the 


FOLIAGE  LEAVES. 


393 


This  is  often  beauti- 


:c 


cells  of  this  layer  are  narrow  and  long, 
fully  shown  when  comparing 
leaves  of  the  same  plant  grown 
in  strong  light  with  those  grown 
in  the  shade.  The  compass 
plant  (Lactuca  scariola)  affords 
an  interesting  example.  The 
leaves  grown  in  the  light  are 
usually  vertical,  so  that  the  light 
reaches  both  sides.  Such  leaves 
often  have  all  of  the  mesophyll 
organized  into  palisade  cells  (fig. 
435),  while  leaves  grown  in  the 
deep  shade  may  have  no  palisade 
cells. 

764.  (2)  Protective  covering. 
— Epidermis  and  cuticle. — The 
walls  of  the  epidermal  cells  are 
much  thickened  in  some  plants. 
Sometimes  this  thickening  occurs 
in  the  outer  wall,  or  both  walls 
may  be  thickened.  Variation  in 
this  respect  as  well  as  the  extent 
of  the  thickening  occur  in  dif- 
ferent plants  and  are  often  corre- 
lated with  the  extremes  of  conditions  which  they  serve  to  meet. 
The  cuticle,  a  waxy  exudation  from  the  thick  wall  of  the  epider- 
mis of  many  leaves,  also  serves  as  a  protection  against  too  great 
loss  of  water,  or  against  the  leaf  becoming  saturated  with  water 
during  rains.  The  cabbage,  carnation,  etc.,  have  a  well-developed 
cuticle.  The  effect  of  the  cuticle  in  shedding  water  can  be  nicely 
shown  by  spraying  water  on  a  cabbage  leaf  or  by  immersing  it  in 
water.  Sunken  stomata  also  retard  the  loss  of  water  vapor. 

Covers  oj  hair  or  scales. — In  many  leaves  certain  of  the  cells 
of  the  epidermis  grow  out  into  the  form  of  hairs  or  scales  of 
vanous  forms,  and  they  serve  a  variety  of  purposes.  iVhen 


Fig-  435- 

Structure  of  leaf  of  Lactuca  scariola. 
Upper  one  grown  in  sunlight,  palisade 
cells  on  both  sides.  Lower  one  grown 
in  shade,  no  palisade  tissue. 


394  RELATION  TO  ENVIRONMENT. 

the  hairs  form  a  felt-like  covering  as  in  the  common  mullein 
some  antennarias,  etc.,  they  lessen  the  loss  of  water  vapor  be' 
cause  the  air-currents  close  to  the  surface  of  the  leaf  are  retarded. 
Spines  (see  the  thistles,  etc.)  also  afford  a  protection  against 
certain  animals. 

765.  (3)  Reduction  of  surface.— Reduction  of  leaf  surface  is 
brought  about  in  a  variety  of  ways.  There  are  two  general 
modes:  (ist)  Reduction  of  surface  along  with  reduction  of 
mass;  (2d)  Reduction  of  surface  inversely  as  the  mass.  Ex- 
amples of  the  first  mode  are  seen  in  the  dissected  leaves  of  many 
aquatic  plants.  In  this  finely  dissected  condition  the  mass  of 
of  the  leaf  substance  is  much  reduced  as  well  as  the  leaf  surface, 
but  the  leaf  is  less  liable  to  be  injured  by  movement  of  the  water. 
In  addition  it  has  already  been  pointed  out  that  lobed  and 
divided  aerial  leaves  are  much  less  liable  to  injury  from  violent 
movements  of  the  air,  than  if  a  leaf  with  the  same  general  out- 
line were  entire.  The  needle  leaves  of  the  conifers  are  also 
examples,  and  they  show  as  well  structural  provisions  for  pro- 
tection in  the  thick,  hard  cell- walls  of  the  epidermis.  To  off- 
set the  reduced  surface  there  are  numerous  crowded  leaves. 
Reduction  of  surface  inversely  as  the  mass,  i.e.,  the  mass  of 
the  leaf  may  not  be  reduced  at  all,  or  it  may  be  more  or  less 
increased.  In  other  words,  there  is  less  leaf  surface  in  pro- 
portion to  the  mass  of  leaf  substance.  It  is  probable  in  many 
cases,  example:  the  crowded,  overlapping  small  scale  leaves  of 
the  juniper,  arbor  vitae,  cypress,  cassiope,  pyxidanthera,  etc.,  that 
there  has  been  a  reduction  in  the  size  of  the  leaf,  and  at  the 
same  time  an  increase  in  thickness.  This  with  the  crowding 
together  of  the  leaves  and  their  thick  cell-walls  greatly  lessens 
the  radiation  of  moisture  and  heat,  thus  protecting  the  leaves 
both  in  dry  and  cold  weather.  The  succulents,  like  " live-for- 
ever," have  a  small  amount  of  surface  in  proportion  to  the  mass 
of  the  leaf.  In  the  yucca,  though  the  leaves  are  often  large, 
they  are  very  thick  and  expose  a  comparatively  small  amount 
of  surface  to  the  dry  air  and  intense  sunlight  of  the  desert  regions. 
The  epidermal  covering  is  also  hard  and  thick.  In  addition, 


FOLIAGE  LEAVES.  395 

such  leaves,  as  well  as  those  of  many  succulents,  are  so  thick 
they  provide  water  storage  sufficient  for  the  plants,  which  radi- 
ate so  slowly  from  their  surface. 

766.  (4)  Elimination  of  the  leaf. — Perhaps  the  most  striking 
illustration  of  the  reduction  of  leaf  surface  is  in  those  cases  where 


Fiy.  436. 

A  "Phylloclade,"  leaves  absent,  stems  broadened  to  function  as  leaves,  on  the 
edges  numerous  flowers  are  borne. 

the  leaf  is  either  completely  eliminated  as  in  certain  euphorbias, 
or  in  certain  of  the  cacti  where  the  leaves  are  thought  to  be  re- 
duced to  spines.  Whether  the  cactus  spine  belongs  to  the  leaf 
series  or  not,  the  leaf  as  an  organ  for  assimilation  and  trans- 
piration has  been  completely  eliminated  and  the  same  is  true 
in  the  phylloclades.  The  leaf  function  has  been  assumed  by 
the  stem.  The  stem  in  this  case  contains  all  the  chlorophyll; 
is  bulky,  and  provides  water  storage. 

III.  Protective  Positions. 

767.  In  many  cases  the  leaves  are  arranged  either  in  relation 
to  the  stem,  or  to  each  other,  or  to  the  ground,  in  such  a  way 
as  to  give  protection  from  too  great  radiation  of  heat  or  moisture. 
In  the  examples  already  cited  the  imbricated  leaves  of  cassiope, 


RELATION   TO  ENVIRONMENT 

pyxidanthera,  juniper,  etc.,  come  also  under  this  head.  In  the 
jumpers  the  leaves  spread  out  in  the  summer,  while  in  the  winter 
they  are  closely  overlapped.  An  interesting  example  of  protective 
position  is  to  be  seen  in  the  case  of  the  leaves  of  the  white  pine. 
During  quite  cold  winter  weather  the  needles  are  appressed  to 
the  stem,  and  sometimes  the  trees  present  a  striking  appear- 
ance in  contrast  with  the  spreading  position  of  the  needles  in 
summer.  On  windy  days  in  winter,  the  needles  turn  with  the 
wind  and  become  rigid  in  that  position  so  that  they  remain 
in  a  horizontal  position  for  some  time,  often  until  the  wind 
dies  down,  or  until  milder  weather.  The  following  day,  should 
there  be  a  cold  strong  wind  from  the  opposite  direction,  the 
needles  again  assume  a  leeward  direction.  In  quiet  weather 
appressed  to  the  stem  and  in  the  form  of  a  brush  there  is  less 
radiation  of  heat  than  if  they  diverged.  In  strong  winds  by 
turning  in  the  leeward  direction  the  wind  is  not  driven  between 
the  needle  bases  and  scales.  Some  plants,  especially  many 
of  those  in  arctic  and  alpine  regions,  have  very  short  stems  and 
the  leaves  are  developed  near  the  ground,  or  the  rock.  Lying 
close  on  the  ground  they  do  not  feel  the  full  force  of  the  drying 
winds,  there  is  less  radiation  from  them,  and  the  radiation  of 
heat  from  the  ground  protects  them.  Many  plants  exhibit 
movement  in  response  to  certain  stimuli  which  place  them  in 
a  position  for  protection.  Some  of  these  examples  have  been 
discussed  under  the  head  of  irritability  (see  Chapter  XIII).  The 
night  position  of  leaves  and  cotyledons  presented  by  many 
plants,  but  especially  by  many  of  the  Leguminosae,  is  brought 
about  by  the  removal  of  the  light  stimulus  at  evening.  In  many 
leaves,  when  the  light  influence  is  removed,  the  influence  of 
growth  turns  the  leaves  downward,  or  the  cotyledons  of  some 
plants  upward.  In  this  vertical  position  of  the  leaf-blade  there 
is  less  radiation  of  heat  during  the  cool  night.  The  most  strik- 
ing cases  of  protection  movements  are  seen  in  the  sensitive 
plant.  As  we  have  seen,  the  leaves  of  mimosa  close  in  a  verti- 
cal position  at  midday  if  the  light  and  heat  are  too  strong.  Ex- 
cessive transpiration  is  thus  prevented.  At  night  the  vertical 


FOLIAGE  LEAVES. 


397 


position  prevents  excessive  radiation  of  heat.  The  vertical  or 
profile  position  of  the  leaves  of  the  compass  plant  already  re- 
ferred to  not  only  lessens  transpiration,  but  the  intense  heat  and 
light  of  the  midday  sun  is  avoided.  This  profile  position  is 
characteristic  of  certain  plants  in  the  dry  regions  of  Australia, 
and  the  topmost  leaves  of  tropical  forests. 

IV.  Relation  of  Leaves  to  Light. 

768.  It  is  very  obvious  from  our  study  of  the  function  of  the 
foliage  leaf  that  its  most  important  relation  to  environment  is 
that  which  brings  it  in  touch  with  light  and  air.  It  is  necessary 
that  light  penetrate  the  leaf  tissue  that  the  gases  of  the  air  and 


Fig.  437 
Mosaic  form  by  trailing  shoots  of  Panicum  variegatum,  "ribbon  grass." 

plant  may  readily  diffuse  and  that  water  vapor  may  pass  out 
of  the  leaf.  The  thin  expanded  leaf-blade  is  the  most  economi- 
cal and  efficient  organ  for  leaf  work. .  We  have  seen  that  leaves 
respond  to  light  stimulus  in  such  a  way  as  to  bring  their  upper 
sides  usually  to  face  the  source  of  light,  at  right  angles  to  it  or 
nearly  so  (heliotropism,  see  Chapter  XIII).  How  fully  this  is 
brought  about  depends  on  the  kind  of  plant,  as  well  as  on  other 
elements  of  the  environment,  for  as  we  have  seen  in  our  study  of 
leaf  protection  there  is  danger  to  some  plants  in  any  region, 


398  RELATION   TO  ENVIRONMENT. 

and  to  other  plants  in  certain  regions  that  the  intense  light 
and  heat  may  harm  the  protoplast,  or  the  chlorophyll,  or  both. 

The  statement  that  leaves  usually  face  the  light  at  right  angles 
is  to  be  taken  as  a  generalized  one.  The  source  of  the  strongest 
illumination  varies  on  different  days  and  again  at  different  times 
of  the  day.  On  cloudy  days  the  zenith  is  the  source  of  strongest 
illumination.  The  horizontal  position  of  a  leaf,  where  there  are 
no  intercepting  lateral  or  superior  objects  would  receive  its 
strongest  light  rays  perpendicular  to  its  surface.  The  fact  is, 
however,  that  leaves  on  the  same  stem,  because  of  taller  or 
shorter  adjacent  stems,  are  so  situated  that  the  rays  of  greatest 
illuminating  power  are  directed  at  some  angle  between  the 
zenith  and  horizon.  Many  leaves,  then,  which  may  have  their 
upper  sides  facing  the  general  source  of  strongest  illumination, 
no  not  necessarily  face  the  sun,  and  they  are  thus  protected 
from  possible  injury  from  intense  light  and  heat  because  the 
direct  rays  of  sunlight  are  for  the  most  part  oblique.  This 
does  not  apply,  of  course,  to  those  leaves  which  "follow  the 
sun"  during  the  day.  Their  specific  constitution  is  such  that 
intense  illumination  is  beneficial. 

The  leaf  is  adjusted  as  well  as  may  be  in  different  species  of 
varying  constitution,  and  under  different  conditions,  to  a  certain 
balance  in  its  relation  to  the  factors  concerned.  The  problem 
then  is  to  interpret  from  this  point  of  view  the  positions  and 
grouping  of  leaves.  Because  of  the  specific  constitution  of  dif- 
ferent plants,  and  because  of  a  great  variety  of  conditions  in  the 
environment,  we  see  that  it  is  a  more  or  less  complex  question. 

769.  Day  and  night  positions  contrasted. — In  many  plants 
the  day  and  night  positions  of  the  leaves  are  different.  At 
night  the  leaves  assume  a  position  more  or  less  vertical,  known 
as  the  profile  position.  This  is  generally  regarded  as  a  pro- 
tective position,  since  during  the  cool  of  the  night  the  radiation 
of  heat  is  less  than  if  the  leaf  were  in  a  vertical  position.  In 
many  of  these  plants,  however,  the  leaves  in  assuming  the  night 
position  become  closely  appressed  which  would  also  lessen  the 
radiation.  This  peculiarity  of  leaves  is  largely  possessed  by 


FOLIAGE  LEAVES. 


399 


the  members  of  the  family  Leguminoseae  (clovers,  peas,  beans, 
etc.),  and  by  the  sensitive  plants.*  But  it  is  also  shared  by 
some  other  plants  as  well  (oxalis,  for  example).  The  leaves 
of  these  plants  are  usually  provided  with  a  mechanism  which 
enables  them  to  execute  these  movements  with  ease.  There  is 
a  cushion  (pulvinus)  of  tissue  at  the  base  of  the  petiole,  and  in 
the  case  of  compound  leaves,  at  the  base  of  the  pinnae  and  pin- 
nules which  undergoes  changes  in  turgor  in  its  cells.  The  col- 
lapsing of  the  cells  by  loss  of  water  into  the  intercellular  spaces 
causes  the  leaf  to  droop.  When  the  cells  regain  their  turgor 
by  the  absorption  of  the  water  from  the  intercellular  spaces  the,, 
leaf  is  raised  to  the  horizontal,  or  day  position.  The  light  stiiru 
ulus  induces  turgor  of  the  pulvinus,  the  disappearance  of  the  stim- 


Fig.  438. 
Sunflower  with  young  head  turned  toward  morning  sun. 

ulus  is  accompanied  by  a  loss  of  turgor.  It  is  a  remarkable 
fact  that  in  some  sensitive  plants,  intense  light  stimuli  are  alarm 
signals  which  result  in  the  same  movement  as  if  the  light  stim- 

*  The  most  remarkable  case  is  that  of  the  "telegraph"  plant  (Des- 
modium  gyrans).  Aside  from  the  day  and  night  positions  which  the 
leaves  assume,  there  is  a  pair  of  small  lateral  leaflets  to  each  leaf  which  con- 
stantly execute  a  jerky  motion,  and  swing  sromid  in  a  circle  like  the  second 
hand  of  a  watch. 


40O 


RELATION   TO  ENVIRONMENT. 


ulus  were  entirely  removed.  As  we  know  also  contact  or  pres- 
sure stimulus,  or  jarring  produces  the  same  result  in  " sensitive" 
plants  like  mimosa,  some  species  of  rubus,  etc.  In  many  plants 
there  is  no  well-developed  pulvinus,  and  yet  the  leaves  show 
similar  movements  in  assuming  the  day  and  night  positions. 
Examples  are  seen  in  the  sunflower,  and  in  the  cotyledons  of 
many  plants.  A  little  observation  will  enable  any  one  interested 
to  discover  some  of  these  plants.*  In  these  cases  the  night 
position  is  due  to  epinastic  growth,  and  while  this  influence  is 
not  removed  during  the  day  the  light  stimulus  overcomes  it 
and  the  leaf  is  raised  to  the  day  position. 

770.  Leaves  which  rotate  with  the  sun,— During  the  growth 
period  the  leaves  of  the  sunflower  as  well  as  the  growing  end 


Fig.  439- 
Same  sunflower  plant  photographed  just  at  sundown. 

of  the  stem  respond  readily  to  the  direct  sunlight.  The  re- 
sponse is  so  complete  that  during  sunny  days  the  leaves  toward 
the  growing  end  of  the  stem  are  drawn  close  together  in  the 
form  of  a  rosette  and  the  entire  rosette  as  well  as  the  end  of  the 


*  Seedlings  are  usually  very  sensitive  to  light  and  are  good  objects  to 
Study. 


FOLIAGE  LEAVES. 


401 


stem  are  turned  so  that  they  face  the  sun  directly.  In  the  morn 
ing  under  the  stimulus  of  the  rising  sun  the  rosette  is  formed 
and  faces  the  east.  All  through  the  day,  if  the  sun  continues  to 
shine,  the  leaves  follow  it,  and  at  sundown  the  rosette  faces 
squarely  the  western  horizon.  For  a  week  or  more  the  young 
sunflower  head  will  also  face  the  sun  directly  and  follow  it  all 
day  as  surely  as  the  rosette  of  leaves.  At  length,  a  little  while 
before  the  flowers  in  the  head  blossom,  the  head  ceases  to  turn, 


Fig.  440. 
Same  plant  a  little  older  when  the  head  does  not  turn,  but  the  stem  and  leaves  do. 

but  the  rosette  of  leaves  and  the  stem  also,  to  some  extent,  con- 
tinue to  turn  with  the  sun.  When  the  leaves  become  mature 
they  also  cease  to  turn.  This  is  well  shown  in  all  three  photo- 
graphs (figs.  438-439).  The  lower  leaves  on  the  stem  being 
older  have  assumed  the  fixed  horizontal  position  usually  char- 
acteristic of  the  plant  with  cylindrical  habit. 

It  is  not  true,  as  is  commonly  supposed,  that  the  fully  opened 
sunflower  head  turns  with  the  sun.  But  I  have  observed  young 
heads  four  or  five  inches  in  diameter  rotate  with  the  sun  all  day. 
This  is  because  the  growing  end  of  the  stem  as  well  as  the  young 
head  responds  to  the  light  stimulus.  So  there  is  some  truth  as 
well  as  a  great  deal  of  fiction  in  the  popular  belief  that  the  sun- 


402  RELATION  TO  ENVIRONMENT. 

flower  head  follows  the  sun.  The  young  head  will  follow  the 
sun  all  day  even  if  all  the  leaves  are  cut  off,  and  the  growing 
stem  will  also  if  all  the  leaves  as  well  as  the  flower  head  are  cut 
away.  Young  seedlings  will  also  turn  even  if  the  cotyledons  and 
plumule  are  cut  off. 

This  phenomenon  of  the  rotation  of  leaves  with  the  sun  is 
much  more  general  than  one  would  infer,  as  may  be  seen  from 
a  little  careful  observation  of  rapidly  growing  plants  on  bright 
sunny  days.  In  Alabama  I  have  observed  beautiful  rosettes  of 
Cassia  marilandica  rotate  with  the  sun  all  day.  The  peculiarity 
is  very  striking  in  the  cotton  plant,  especially  when  the  rows 
extend  north  and  south.  In  the  forenoon  or  afternoon  it  is 
most  striking  as  the  entire  row  shows  the  leaves  tilted  up  facing 
the  sun.  There  are  many  of  our  weeds  and  common  flowers 
of  field  and  garden  which  show  this  rotation  of  the  leaves.  Some 
of  these  form  rotating  rosettes;  while  in  others  the  leaves  rotate 
independently  as  in  the  sweet  clover. 

771.  Fixed  position  of  old  leaves.— In  many  of  the  cases  cited 
in  the  preceding  paragraph,  the  rotation  of  the  leaf  only  occurs 
on  sunny  days.     During  cloudy  days  the  leaves  of  the  sunflower, 
for  example,  are  in  a  nearly  horizontal  position,  or  the  lower 
ones  may  be  somewhat  oblique,  since  the  stronger  illumination  on 
such  a  plant  would  be  the  oblique  rays  rather  than  the  zenith 
rays.     As  the  leaves  reach  maturity  also  the  epinasitic  growth  is 
equalized  by  hyponastic  growth  so  that  the  growth  movements 
bring  the  leaf  to  stand  in  a  nearly  horizontal  position,  or  that 
position  in  which  it  receives  the  best  illumination.     In  age,  then, 
many  leaves  have  a  fixed  position  and  this  corresponds  with  the 
position  assumed  on  cloudy  days. 

772.  Position  on  horizontal  stems. — On  horizontal  stems  the 
leaves  have  a  horizontal  position,  and  if  such  a  stem  is  stood  in 
an  erect  position  the  appearance  is  very  odd.     If  the  leaf  arises 
directly  from  the  horizontal  stem,  its  petiole  will  be  twisted  part 
way  around  in  order  to  bring  the  face  of  the  leaf  uppermost. 
It  is  interesting  to  observe  the  different  relation  of  stem,  petiole 
and  blade  and  the  amount  of  twisting  as  the  horizontal  stem  or 


FOLIAGE  LEA  VES.  4°3 

vine  trails  over  irregularities  in  the  surface,  or  climbs  over  and 
through  other  vegetation. 

773.  Position  of  leaflets  on  divided  leaves.— An  interesting 
comparison  can  be  made  with  entire,  lobed,  divided  and  dis- 
sected leaves.  The  entire  leaf  usually  lies  in  one  plane,  since 
usually  the  problem  of  adjustment  is  the  same  for  the  entire 
surface.  So  the  lobes  of  a  leaf  usually  lie  all  in  the  same  plane 
as  they  would  if  the  leaf  were  entire.  We  find  the  same  is  true 
usually  of  the  compound  leaf.  It  forms  an  incomplete  mosaic. 
Some  of  the  pieces  having  been  removed  allow  much  of  the  light 
to  pass  through  to  leaves  beneath.  Leaves,  especially  those  of 
some  size  rarely  lie  in  a  fiat  plane.  Some  are  more  or  less  de- 
pressed. Some  curve  downward.  Compound  leaves  often 
curve  more  or  less  and  the  leaflets  often  droop  more  or  less  in  a 
graceful  fashion.  It  is  interesting,  however,  that  these  far-sepa- 
rated leaflets  all  lie  in  the  same  general  plane.  This  is  because 
the  area  of  the  leaf,  if  not  too  large,  makes  the  problem  of  posi- 
tion with  reference  to  light  much  the  same  as  if  the  leaf  were 
entire.  The  leaflets  or  divisions,  though  separated,  are  laminate, 
and  they  can  work  more  efficiently  facing  the  light.  But  suppose 
we  extend  our  observation  to  the  finely  dissected  capillary  leaves 
of  some  of  the  parsley  family  (Umbelliferae),  or  to  the  upper 
leaves  of  the  fennel-leaved  thoroughwort  (Eupatorium  fceni- 
culaceum)  among  the  aerial  plants,  and  to  Myriophyllum  among 
the  aquatic  plants.  The  divisions  are  threadlike  or  cylindrical. 
One  side  of  the  leaflet  is  just  as  efficient  when  presented  to  the 
light  as  another.  As  a  result  the  leaflets  are  not  arranged  in 
the  same  plane,  but  stand  out  in  many  directions. 

Occasionally  one  finds  a  divided  or  compound  leaf  in  such  a 
position  that  one  portion,  because  of  being  shaded  above,  receives 
the  stronger  light  stimulus  from  the  side,  while  the  other  portion 
is  lighted  from  above.  If  this  relation  continues  throughout 
the  growth-period  of  the  leaf  the  leaflets  of  one  portion  may  lie 
in  a  different  plane  from  those  of  the  other  portion.  In  such 
cases,  some  of  the  leaflets  are  permanently  twisted  to  bring  them 
into  their  proper  light  relation. 


404  RELATION   TO  ENVIRONMENT. 

V.  Leaf  Patterns. 

MOSAICS,    OB   CLOSE   PATTERNS. 

774.  Where  the  leaves  of  a  plant,  or  a  portion  of  a  plant,  are 
approximate  and  arranged  in  the  form  of  a  pattern,  the  leaves 
fitting  together  to  form  a  more  or  less  even  and  continuous  sur- 
face, such  patterns  are  sometimes  termed  "mosaics,"  since  the 
relation  of  leaves  to  one  another  is  roughly  like  the  relation  of 
the  pieces  of  a  mosaic.  A  good  illustration  of  a  mosaic  is  pre- 
sented by  a  greenhouse  plant  Fittonia  (fig.  441).  The  stems 


Fig.  441. 

^  Fittonia  showing  leaves  _  arranged  to  form  compact  mosaic.     The  netted  vena- 
tion of  the  leaf  is  very  distinctly  shown  in  this  plant.     (Photo  by  the  Author.) 

are  prostrate  and  the  erect  branches  quite  short,  but  it  may 
have  quite  a  wide  system  by  the  spreading  of  the  runners;  the 
branches  of  such  a  length  that  the  leaves  borne  near  the  tips  all 
fit  together  forming  a  broad  surface  of  leaves  so  closely  fitted 
together  often  that  the  stems  cannot  be  seen.  The  advantage 
of  a  mosaic  over  a  separate  disposition  of  leaves  at  somewhat 
different  levels  is  that  the  leaves  do  not  shade  one  another.  Were 
all  the  light  rays  coming  down  at  right  angles  to  the  leaves,  there 
would  not  be  any  shading  of  the  lower  ones,  but  the  oblique 
rays  of  light  would  be  cut  off  from  many  of  the  leaves.  In  the 
case  of  a  mosaic  all  the  rays  of  light  play  upon  all  the  leaves. 
Some  of  the  mosaics  which  can  be  observed  are  as  follows: 


FOLIAGE  LEAVES. 


405 


775.  Rosette  pattern. — The  rosette  pattern  is  presented  by 
many  plants  with  "radial"  leaves,  or  leaves  which  arise  in  a 
cluster  near  the  surface 
of  the  ground,  and  are 
thus  more  or  less  crowded 
in  their  arrangement  on 
the  stem.  The  pretty 
gloxinia  often  presents 
fine  examples  of  a  loose 
rosette.  In  the  rosette 
pattern  the  petioles  of 
the  lower  leaves  are 
longer  than  the  upper 
ones,  and  the  blade  is 
thus  carried  out  beyond 
the  inner  'eaves.  The 
leaves  being  so  crowded 
in  their  attachment  to 


Fig.  442. 
Rosette  pattern  of  leaves. 


the  stem  lie  very  nearly 
in  the  same  plane. 

776.  Vines  and  climbers.— Some  of  the  most  extensive  mosaic 
patterns  are  shown  in  creeping  and   climbing  vines.     A  very 
common  example  is  that  of  the  ivies  trained  on  the  walls  of  build- 
ings, covering  in  some  instances  many  square  yards  of  surface. 
Where  the  vines  trail  over  the  ground  or  clamber  over  other 
vegetation,, it  is  interesting  to  observe  the  various  patterns,  and 
the  distortion  of  petioles  brought  about  by  turning  of  the  leaves. 
Of  examples  found  in  greenhouses,  the  Pellonia  is  excellent,  and 
the  trailing  ribbon-grass  often  forms  loose  mosaics. 

777.  Branch   patterns. — These    patterns    are  very  common. 
They  are  often  formed  in  the  woods  on  the  ends  of  branches  by 
the  leaves  adjusting  themselves  so  as  to  largely  avoid  shading 
each  other.     Figure  443  illustrates  one  of  them  from  a  maple 
branch.     It  is  interesting  to  note  the  way  in  which  the  leaves 
fit  themselves  in  the  pattern,  how  in  some  the  petioles  have 
elongated,    while   others   have   remained   short.     Of   course,   it 


406 


RELATION   TO  ENVIRONMENT. 


Fig.  443- 
Spray  of  leaves  of  striped  maple,  showing  different  lengths  of  leafstalks. 


Fig.  444. 
Cedar  of  Lebanon,  strong  light  only  from  one  side  of  tree  (Syria). 


FOLIAGE  LEAVES. 


407 


should  be  understood  that  the  pattern  is  made  during  the  growth 
of  the  leaves. 

778.  The   tree  pattern. — Mosaics  are   often  formed  by  the 
exterior  foliage  on  a  tree,  though  they  are  rarely  so  regular  as 
some  of  those  mentioned  above.     Still  it  is  common  to  see  in  some 
trees  with  drooping  limbs  like  the  elm,  beautiful  and  large  mo- 
saics.    The   weeping   elm   sometimes   forms   a   very   close   and 
quite  even  pattern  over  the  entire  outer  surface.     In  most  trees 
the  leaf  arrangement  is  not  such  as  to  form  large  patterns,  but 
is  more  or  less  open.     While  the  conifers  do  not  form  mosaics 
there  are  many  interesting  examples  of  grouping  of  foliage  on 
branch  systems  into  broadly  expanded  areas,   as   seen  in  the 
branches  of  white  pine  trees,  especially  in  the  edge  of  a  wood, 
or  as  seen  in  the  arbor  vitae. 

OTHER  PATTERNS. 

779.  Imbricate  pattern  of  short  stems.— This  pattern  is  quite 
common,  and  differs  from  the  rosette  in  that  the  leaves  are  dis- 
tributed further  apart  on 

the  stem  so  that  the  cen- 
tral ones  are  consider- 
ably higher  up  than  in 
the  mosaic.  The  lower 
petioles  are  longer,  as  in 
the  rosette,  so  that  the 
outer  lower  leaves  ex- 
tend further  out.  Some 
begonias  show  fine  im- 
bricate patterns. 

780.  Spiral  patterns. 
— They  are  very  common 
on  stems  of  the  cylindrical 

type,  which  are  unbranched,  or  but  little  branched.  The  sun- 
flower, mullein,  chrysanthemum,  as  it  is  grown  in  greenhouses,  the 
Easter  lily,  etc.,  are  examples.  The  spiral  arrangement  of  the 
leaves  provides  that  each  successive  leaf  on  the  stem,  as  one  ascends 
the  stem,  is  a  little  to  one  side  so  that  it  does  not  cast  shade  on  the 


Fig.  445- 
Imbricate  pattern  of  leaves;  Begonia. 


408 


RELATION    TO   ENVIRONMENT. 


leaf  just  below.  In  some  stems,  according  to  the  leaf  arrange- 
ment (or  phyllotaxy),  one  would  pass  several  times  around  in 
ascending  the  stem  before  a  leaf  would  be  found  directly  above 
another,  which  would  be  such  a  distance  below  that  it  would  not 
be  shaded  to  an  appreciable  extent.  Interesting  observations 
can  be  made  on  different  plants  to  work  out  the  relation  of  dis- 
tance of  leaves  on  the  stem  to  length  of  the  upper  and  lower 


m  *s 


Fig.  446. 

Palm  showing  radiate  arrangement  of  leaves  and  the  petiole  of  the  leaf  func- 
tions as  stem  in  lifting  leaf  to  the  light. 

leaves;  the  number  of  vertical  rows  on  the  stem  compared  to 
the  width  of  the  leaves;  and  the  relation  of  these  facts  to  the 
problem  of  light  supply.  Related  to  the  spiral  pattern  is  that  of 
erect  stems  with  opposite  leaves.  Here  each  pair  is  set  at  right 
angles  to  the  direction  of  the  pair  above  or  below. 

781.  Radiate  pattern. — This  pattern  is  present  in  many  grasses 
and  related  plants  with  narrow  leaves  and  short  stems.  The 
leaves  are  often  very  crowded  at  the  base,  but  by  radiating  in 
all  directions  from  the  horizontal  to  the  vertical,  abundant  ex- 


FOLIAGE  LEAVES.  409 

posure  to  light  is  gained  with  little  shading.     The  dragon  tree 
screw-pine,  and  plants  grown  in  greenhouses  also  illustrate  this 


Fig.  447- 
Screw  pine  (Pandanus)  showing  prop  roots  and  radiate  pattern  of  leaves. 

type.    It  is  also  shown  in  cycads,  palms,  and  many  ferns,  although 
these  have  divided  leaves. 

782.  Compass  plants. — These  plants  with  vertical  leaf  arrange- 
ment, and  exposure  of  both  surfaces  to  the  lateral  rays  of  light 
have  been  mentioned  in  other  sections  (Lactuca    scariola). 

783.  Open  patterns. — Open  patterns  are  presented  by  divided 
or  "branched"  leaves.     Where  the  leaves  are  very  finely  dis- 
sected, they  may  be  clustered  in  great  profusion  and  yet  admit 
sufficient  light  for  some  depth  below.     Where  the  leaflets  are 
broader,  the  leaves  are  likely  to  be  fewer  in  number  and  so 
arranged  as  to  admit  light  to  a  great  depth  so  that  successive 
leaves  below  on  the  same  or  adjacent  stems  may  not  be  too  much 
shaded.     On  such  plants,  often  the  leaves  lying  next  the  ground 
are  entire  or  less  divided. 


CHAPTER  XLI. 

THE   ROOT 
I.  Function  of  Roots. 

784.  The  most  obvious  function  of  the  roots  of  ordinary  plants 
are  two:  ist,  To  furnish  anchorage   and   partial  support,  and 

^2d,  absorption  of  liquid  nutriment  from  the  soil.  The  environ- 
mental relation  of  such  roots,  then,  in  broad  terms,  is  with  the 
soil.  It  is  very  clear  that  in  some  plants  the  root  serves  both 
functions,  while  in  other  plants  the  root  may  fulfil  only  one  of 
these  requirements. 

The  problems  which  the  plant  has  to  solve  in  working  out 
these  relations  are: 

(1)  Permeation  of  the  soil  or  substratum. 

(2)  Grappling  the  substratum. 

(3)  A  congenial  moisture  or  water  relation. 

(4)  Distribution  of  roots  for  the  purpose  of  reaching  food- 
laden  soil. 

(5)  Exposure  of  surface  for  absorption. 

(6)  The  renewal  of  the  delicate  structures  for  absorption. 

(7)  Aid  in  preparation  of  food  from  raw  material. 

(8)  The   maintenance   of  the  required   balance   between  the 
environment  as  a  whole  and  the  increasing  or  changing  require- 
ments of  the  plant. 

785.  (i)  Permeation  of  the  soil  or  substratum. — The  funda- 
mental divergence  of  character  in  the  environmental  relations  of 
root  and  stem  are  manifest  as  soon  as  they  emerge  from  the 
germinating  seed.     Under  the  influence  of  the  same  stimulus 
(gravity)  the  root  shows  its  geotropic  character  by  growing  down- 

410 


ROOTS.  411 

ward,  while  the  geotropic  character  of  the  stem  is  shown  in  its 
upward  growth. 

The  medium  which  the  root  has  to  penetrate  offers  consider- 
able resistance,  and  the  form  of  the  root  as  well  as  its  manner  of 
growth  is  adapted  to  overcome  this  difficulty.  The  slender, 
conical,  penetrating  root-tip  wedges  its  way  between  the  minute 
particles  of  soil  or  into  the  minute  crevices  of  the  rock,  while 
the  nutation  of  the  root  enables  it  to  search  for  the  points  of  least 
resistance.  The  root-tips  having  penetrated  the  soil,  the  older 
portions  of  the  root  continue  this  wedge  action  by  growth  in 
diameter,  though,  of  course,  elongation  of  the  old  parts  of  the 
root  does  not  take  place.  It  is  the  widening  growth  of  the  taper- 
ing root  that  produces  the  wedge-like  action.  The  crevices  of 
the  rock  are  sometimes  broadened,  but  the  resistance  here  is  so 
great,  the  root  is  often  greatly  flattened  out. 

786.  (2)  Grappling  the  substratum.— The  mere  penetration 
of  a  single  root  into  the  soil  gives  it  some  hold  on  the  soil  and  it 
offers  some  resistance  to  a  "pull"  since  it  has  wedged  its  way  in 
and  the  contact  of  soil  particles  offers  resistance.     The  root-hairs 
formed  on  the  first  entering  root  growing  laterally  in  great  num- 
bers and  applying  themselves  very  closely  to  the  soil  particles, 
increase  greatly  the  hold  of  the  plant  on  the  soil,  as  one  can 
readily  see  by  pulling  up  a  young  seedling.     Lateral  roots  are 
soon  formed,  and  as  these  continue  to  extend  and  ramify  in  all 
directions,  the  hold  is  increased  until  in  the  case  of  some  of  the 
larger  plants  the  resistance  their   hold  would  offer  would  equal 
many  tons.      Even  in  some  of  the  smaller  shrubs  and  herbs  the 
resistance  is  considerable,  as  one  can  easily  test  by  pulling  with 
the  hand.     To  obtain  some  idea  of  the  amount  of  resistance  the 
roots  of  these  smaller  plants  offer,  they  can  be  tested  by  pulling 
with  the  ordinary  spring  scales. 

787.  (3)  A  congenial  moisture,  or  water  relation.— In  gen- 
eral, the  roots  seek  those  portions  of  the  soil  provided  with  a  modi- 
cum of  moisture.     Usually  a  suitable  moisture  condition  is  present 
in  those  portions  of  the  soil  containing  the  plant  food.     But  if  por- 
tions of  the  soil  are  too  dry  and  very  nearby  other  portions  con- 


412  RELATION   TO  ENVIRONMENT. 

taining  moisture,  the  roots  grow  mainly  into  the,  moist  substratum 
(hydrotropism).  If  the  soil  is  too  wet,  the  roots  grow  away  from 
it  to  soil  with  less  water,  or  in  some  cases  will  grow  to  and  upon 
the  surface  of  the  soil. 

The  roots  need  aeration,  and  where  the  supply  of  water  is  too 
great,  the  air  is  shut  out,  and  we  know  that  corn,  wheat,  and 
many  other  plants  become  "sickly"  in  low  and  undrained  soil 
in  wet  seasons.  This  can  only  be  said  in  the  case  of  our  ordinary 
dry  land  plants,  i.e.,  those  that  occupy  an  intermediate  position 
between  water-loving  plants  and  dry-conditioned  plants.  This 
phase  of  the  subject  must  be  reserved  for  special  treatment. 
(See  Chapters  XLVI,  XLVII.) 

788.  (4)  Distribution  of  roots  for  the  purpose  of  reaching 
food-laden  soil. — This  is  one  of  the  essential  relations  of  the  root 
in  the  case  of  the  land  plant,  and  probably  accounts  for  the  very 
extensive  ramification  of  the  roots.  To  some  extent  it  also 
explains  the  different  root  systems  in  some  plants.  The  pines, 
spruces,  etc.,  usually  grow  in  regions  where  the  soil  is  very  shal- 
low. The  root  system  does  not  extend  deeply  into  the  soil.  It 
spreads  laterally  and  extends  widely  through  the  shallow  surface 
soil  and  presents  a  very  different  aspect  from  the  stem  system  in 
the  air.  The  root-system  of  the  broad-leaved  trees  usually  extends 
more  deeply  into  the  soil,  while  of  course,  extending  laterally 
to  great  distances.  The  hickory,  walnut,  etc.,  especially  have 
strong  tap  roots  which  extend  deeply  into  the  soil,  and  the  root 
system  of  such  a  tree  is  more  comparable  in  aspect,  if  it  were 
entirely  uncovered,  to  the  stem  system  in  the  air.  The  tap-root 
is  more  pronounced  in  some  trees  than  in  others.  It  may  be  that 
in  the  hickory  and  walnut  the  deep  tap-root  is  important  in 
supplying  the  tree  with  water  in  dry  seasons,  especially  when 
growing  on  dry,  gravelly  soil  which  does  not  retain  moisture  on 
the  surface  nor  hold  it  within  two  or  three  feet  of  the  surface. 
Experiment  has  demonstrated,  by  pot  culture  of  plants,  that 
where  soil  rich  in  plant  food  lies  adjacent  to  poor  soil,  no  matter 
in  what  part  of  the  pot  the  rich  soil  is,  the  greatest  growth  and 
branching  of  roots  is  in  the  rich  soil. 


ROOTS.  4*3 

789.  (5)  Exposure  of  root  surface  for  absorption.-— The  prin- 
cipal part  of  root  absorption  takes  place  in  the  young  root  and 
the  root  hairs  growing  near  the  root-tip.     The  root-tips  and 
root-hairs  in  their  relation  to  the  root  systems  on  which  they  are 
borne  are  not  to  be  compared  morphologically  with  the  leaves 
and  stem  system.     But  the  root-tips  and  hairs  are  absorbing 
organs  of  the  roots  wrhile  the  main  root  system  supports  them, 
brings  them  into  relation  with  the  soil  and  moisture,  and  con- 
ducts food  and  other  substances  to  and  from  them.     One  of  the 
important  relations  of  the  leaf  is  that  of  light,  and  since  the  source 
of  light  is  restricted,  i.e.,  it  is  not  equally  strong  from  all  sides, 
an  expanded  and  thin  leaf-blade  is  more  effective  than  an  equal 
expenditure  of  plant  material  in  the  form  of  thread-like  out- 
growths.    It  is  different,  however,  with  the  plant  food  dissolved 
in  the  soil  water.     It  is  equally  accessible  on  all  sides.     A  greater 
surface  for  absorption  is  exposed  with  the  same  expenditure  of 
material  by  multiplication  of  the  organs  and  a  reduction  in  their 
size.     Numerous  delicate  root-hairs  present  a  greater  absorbing 
surface  than  if  the  same  amount  of  material  were  massed  into 
leaflike    expansions.     There    is    another    important    advantage 
also.     Its  slender  roots  and  thread-like  root-hairs  allow  greater 
freedom  of  circulation  of  water,  food  solutions,  and  air  than  if 
the  absorbing  organs  of  the  roots  were  broadly  expanded. 

790.  (6)  The  renewal  of  the  delicate  structures  for  absorp- 
tion.— The    delicate    root-hairs   are    easily   injured.     The  thin 
cell-walls  through  which  food  solutions  flow  become  more  or  less 
choked  by  the  gradual  deposit  of  substances  in  solution  in  the 
water,  and  continued  growth  of  the  root  in  diameter  forms  a 
firmer  epidermis  and  cortex  through  which  the  solutions  taken 
up  by  the  root-hairs  would  pass  with  difficulty.     For  this  reason 
new  root-hairs  are  constantly  being  formed  on  the  growing  root- 
tip  throughout  the  growing  season,  and  in  the  case  of  perennial 
plants,  through  each  season  of  their  growth. 

791.  (7)  Aid  in  preparation  of  food  from  raw  materials. — For 
most  plants  the  food  obtained  from  the  soil  is  already  in  solution  in 
the  soil  water.     But  there  are  certain  substances  (examples,  some 


RELATION   TO   ENVIRONMENT. 

of  the  chemical  compounds  of  potash,  phosphoric  acid,  etc.)  which 
are  insoluble  in  water.  Certain  acids  excreted  by  the  roots  aid 
in  making  these  substances  soluble  (see  Chapter  III).  In  a  num- 
ber of  plants  the  roots  have  become  associated  with  fungus  or 
bacterial  organisms  which  assist  in  the  manufacture  of  nitro- 
genous food  substances,  or  even  in  the  absorption  of  ordinary 
food  solution  from  the  soil,  or  in  making  use  of  the  decaying 
humus  of  the  forest  (see  Chapter  IX). 

792.  (8)  The  maintenance  of  the  required  balance  between 
the  environment  and  the  increasing  or  changing  requirements 
of  the  plant. — In  this  matter  the  entire  plant  participates.  Men- 
tion is  made  here  only  of  the  general  relation  which  the  root 
sustains  to  its  own  environment  and  the  increased  burden  placed 
upon  it  by  the  shoot.  The  increase  in  the  root  system  keeps 
pace  with  the  increasing  size  of  the  stem  system.  The  roots 
become  stronger,  their  ramifications  wider,  and  the  number  of 
absorbing  rootlets  more  numerous.  The  observation  is  some- 
times offered  that  the  correlation  between  the  root  system  of  a 
plant,  and  the  form  of  the  stem  system  and  position  of  the  leaves, 
is  of  such  a  nature  that  plants  with  a  tap-root  system  have  their 
leaves  so  arranged  as  to  shed  the  water  to  the  center  of  the  sys- 
tem, while  plants  with  a  fibrous  root  system  have  their  leaves  so 
arranged  as  to  shed  the  water  outward.  In  support  of  this 
attention  is  called  to  the  radiate  type  of  the  leaf  system  of  the 
dandelion,  beet,  etc.  In  the  second  place  the  imbricate  type  as 
manifested  in  broad-leaved  trees,  and  in  the  overlapping  branch 
systems  of  many  pines,  etc.  One  should  note,  however,  that  in 
the  former  class  the  leaves  are  often  arranged  to  shed  as  much 
water  outward  as  inward.  As  to  the  latter  class,  there  is  need 
of  experiment  to  determine  whether  these  empirical  observations 
are  correct,  for  the  following  reasons:  ist,  Root  and  leaf  distri- 
bution are  governed  by  other  and  more  important  laws,  the  root 
being  influenced  by  the  location  of  food  in  the  soil  which  usually 
forms  a  very  thin  stratum  while  the  shoot  and  leaf  is  mainly  in- 
fluenced by  light,  and  root  distribution  is  much  wider  in  a  lateral 
direction  than  that  of  the  branches.  2d,  In  light  rains  the  leaf 


ROOTS.  4J5 

surface  holds  back  practically  all  the  rain  which  is  then  evap- 
orated into  the  air  and  lost  to  the  root  systems.  3d,  In  heavy 
and  long-continued  rains  the  water  breaks  through  the  leaf 
system  to  such  an  extent  that  roots  under  the  tree  would  be  as 
well  supplied  as  those  outside,  and  the  ground  outside  being 
saturated  anyway,  the  roots  do  not  need  the  small  additional 
water  which  may  have  been  shed  outward.  4th,  It  is  the  habit 
of  plants  where  left  undisturbed  (except  in  rare  cases),  to  grow 
in  more  or  less  dense  formations  or  societies.  Here  there  is  no 
opportunity  for  any  appreciable  centrifugal  distribution  of  rain- 
fall and  yet  the  root  distribution  is  practically  the  same,  except 
that  the  root  systems  of  adjacent  plants  are  interlaced. 

II.  Kinds  of  Roots. 

793.  The  root  system.— From  the  foregoing,  it  will  be  under- 
stood that  the  roots  of  a  plant  taken  together  form  the  root  sys- 
tem of  that  plant.     In  soil  roots  in  general  we  usually  recognize 
two  kinds  of  root  systems. 

794.  The  fibrous-root  system. — Roots  which  are  composed  of 
numerous    slender    branching    roots    resembling    "fibers,"    are 
termed  fibrous,  or  the  plant  is  said  to  have  a  fibrous-root  system, 
The  bean,  corn,  most  grasses,  and  many  other  plants  have  fibrous- 
root  systems. 

795.  The  tap-root  system.— Plants  with  a  recognizable  cen- 
tral  shaft-like   root,   more   or   less   thickened   and   considerably 
stouter  than  the  lateral  roots,  are  said  to  have  tap  roots,  or  they 
htv/e  a  tap-root  system.     The  dandelion,  beet,  carrot  (see  crown 
tuber)    are   examples.     The   hickory,    walnut,   and   some   other 
trees  have  very  prominent  tap-roots  when  young.     The  tap-root 
is  maintained  in  old  age,  but  the  lateral  roots  often  become 
finally  as  large  as  the  tap-root.     Besides  tap-roots  and  fibrous- 
roots,  which  include  the  larger  number,  several  other  kinds  of 
roots  are  to  be  enumerated. 

796.  Aerial  roots.— Aerial  roots  are  most  abundantly  devel- 
oped in  certain  tropical  plants,  especially  in  the  orchids  and 
aroids.     Many  examples  of  these  nlants  are  grown  in  conserva- 


416 


RELATION    TO  ENVIRONMENT. 


tones.  The  amount  of  moisture  is  so  great  in  these  tropical 
regions  that  the  roots  are  abundantly  supplied  without  the  soil 
relation.  Certain  of  the  roots  hang  free  in  the  air  and  are  pro- 
vided with  a  special  sheath  of  spongy  tissue  called  the  velamen, 
through  which  moisture  is  absorbed  from  the  air.  Other  roots 
attach  themselves  to  the  trunk  or  branches  of  the  tree  on  which 
the  orchid  is  growing,  and  furnish  the  support  to  the  epiphyte, 
as  such  plants  are  often  called.  Among  the  tangle  of  these 
clinging  roots  falling  leaves  are  caught.  Here  they  decay  and 
nourishing  roots  grow  from  the  clinging  roots  into  this  mass  of 
decaying  leaves  and  supply  some  of  the  plant  food.  Aerial 
roots  sometimes  possess  chlorophyll. 

There  are  a  number  of  plants,  however,  in  temperate  regions 
which  have  aerial  roots.  These  are  chiefly  used  to  give  the  stem 
support  as  it  climbs  on  trees  or  on  walls.  They  are  sometimes 
called  clinging  roots.  A  common  example  is  the  climbing  poison 
ivy  (Rhus  radicans),  the  trumpet  creeper,  etc.  Such  aerial  roots 
are  called  adventitious  roots. 

797.  Bracing  roots,  or  prop  roots. — These  are  developed  in  a 
great  variety  of  plants  and  serve  to  brace  or  prop  the  plant  where 

the  fibrous-root  system  is  in- 
sufficient to  support  the  heavy 
shoot  system,  or  the  shoot  sys- 
tem branches  so  widely  props 
are  needed  to  hold  up  the 
branches.  In  the  common  In- 
dian corn  several  whorls  of 
bracing  roots  arise  from  the 
nodes  near  the  ground  and  ex- 
KrT  tend  outward  and  downward  to 
the  ground,  though  the  upper 
whorls  do  not  always  succeed  in 
reaching  the  ground.  The 
screw-pine  so  common  in 
greenhouses  affords  an  excellent  example  of  prop  roots.  The 
roots  are  quite  large,  and  long  before  the  root  reaches  the  soil  the 


Fig.  448. 
Bracing  roots  of  Indian  corn. 


ROOTS.  417 

large  root-cap  is  evident.  The  banyan  tree  of  India  is  a  classic 
example  of  prop  roots  for  supporting  the  wide-reaching  branches. 
The  mangrove  in  our  own  subtropical  forests  of  Florida  is  a 
nearer  example. 

798.  Buttresses  are  formed  at  the  junction  of  the  root  and 
trunk,   and  therefore  are  part  root  and  part  stem.     Splendid 


Fig.  449. 
Buttresses  of  silk-cotton  tree,  Nassau. 

examples  of  buttresses  are  formed  on  the  silk-cotton  tree.  They 
are  sometimes  formed  on  the  elm  and  other  trees  in  low  swampy 
ground. 

799.  Fleshy  roots,  or  root  tubers. — These  are  enlargements  of 
the  root  in  the  form  of  tubers,  as  in  the  sweet  potato,  the  dahlia, 
etc.     They  are  storage  reservoirs  for  food.     Portions  of  the  roots 
become  thick  and  fleshy  and  contain  large  quantities  of  sugar, 
as  in  the  sweet  potato,  or  of  inulin  (a  carbohydrate)  in  the  root- 
tubers  of  the  dahlia  and  other  composites. 

800.  Water  roots  and  roots  of  water  plants. — These  are  roots 
which  are  developed  in  the  water,  or  in  the  soil.     Water-roots 
are  sometimes  formed  on  land  plants  where  the  root  comes  in 


41 8  RELATION   TO  ENVIRONMENT. 

contact  with  a  body  of  water,  or  a  stream.  Water-roots  usually 
possess  no  root-hairs,  or  but  a  few,  as  can  be  seen  by  comparing 
water-roots  with  soil-roots,  or  by  comparing  roots  of  plants 
grown  in  water  cultures.  The  greater  body  of  water  in  contact 
with  the  root  and  the  more  delicate  epidermis  of  the  root  render 
less  necessary  the  root-hairs.  The  duck-meats  (Lemna)  are 
good  examples  of  plants  having  only  water-roots.  Other  aquatic 
plants  like  the  potamogetons,  etc.,  have  true  roots  which  grow 
into  the  soil  and  serve  to  anchor  the  plant,  but  they  are  not  devel- 
oped as  special  organs  of  absorption,  since  the  stem  and  leaves 
largely  perform  this  function. 

801.  Holdfasts. — These  are  organs  for  anchorage  which  are 
not  true  roots.     These  are  especially  well  developed  in  some  of 
the   algae    (Fucus,   Laminaria,   etc.).     They  are   usually   called 
holdfasts.     The   holdfasts   of   the   larger   algae   are   mainly   for 
anchoring  the  plant.     They  do  not  function  as  absorbing  organs, 
and  the  structure  is  different  from  that  of  true  roofs. 

802.  Haustoria  or  suckers  is  a  name  applied  to  another  kind 
of  holdfast  employed  by  parasitic  plants.     In  the  dodder  the 
haustorium  penetrates  the  tissue  of  the  host  (the  plant  on  which 
the  parasite  grows),  and  besides  furnishing  a  means  of  attach- 
ment, it  serves  as  an  absorbing  organ  by  means  of  which  the 
parasite  absorbs  food  from  its  host.     The  parasitic  fungi  like 
the  powdery  mildews  which  grow  on  the  surface  of  their  hosts 
have  simple  haustoria  which  serve  both  as  organs  of  attachment 
and  absorption,  while  in  the  rusts  which  grow  in  the  interior  of 
their  hosts  the  haustoria  are  merely  absorbing  organs. 

803.  Rootlets,  or  rhizoids. — Many  of  the  algae,  liverworts  and 
mosses  have  slender,  hair-like  organs  of  attachment  and  absorp- 
tion.    These  plants  do  not  have  true  roots.     Because  of  the 
slender  form  and  small  size  of  these  organs,   they  are  called 
rhizoids,  or  rootlets.     In  form  many  of  them  resemble  the  root- 
hairs  of  higher  plants. 


CHAPTER  XLII. 

THE    FLORAL   SHOOT. 

I.  The  Parts  of  the  Flower. 

THE  portion  of  the  stem  on  which  the  flowers  are  borne  is 
the  flower  shoot  or  axis,  or  taken  together  with  the  flowers,  it  is 
knowr  as  the  Flower  Cluster. 

804 ,  The  flower. — The  flower  is  best  understood  by  an  exam- 
ination, first  of  one  of  the  types  known  as  a  "  complete r>  flower, 
as  in  the  buttercup,  the  spring  beauty,  the  bloodroot,  the  apple, 
the  rose,  etc. 

There  are  two  sets  of  organs  or  members  in  the  complete 
flower — (i)  the  floral  envelope;  (2)  the  essential  or  necessary 
merQbers  or  organs. 

Tfrf^loral  envelope  when  complete  consists  of — ist,  an  outer 
envelope^  the  calyx,  made  up  of  several  leaflike  structures 
(sepals),  very  often  possessing  chlorophyll,  which  envelop  all 
the  other  parts  of  the  flower  when  in  bud ;  2d,  an  inner  envelope, 
the  corolla,  also  made  up  of  several  leaflike  parts  (petals),  usu- 
ally bright  colored  and  larger  than  the  sepals.  The  outer  and 
inner  floral  envelopes  are  usually  in  whorls  (though  in  close  spirals 
in  many  of  the  buttercup  family,  etc.),  and  for  reasons  discussed 
elsewhere  (Chapter  XXXIV)  represent  leaves.  The  essential 
or  necessary  members  of  the  flower  are  also  usually  in  whorls 
and  likewise  represent  leaves,  but  only  in  rare  cases  is  there  any 
suggestion,  either  in  their  form  or  color,  of  a  leaf  relationship. 
These  members  are  in  two  sets:  (i)  The  outer,  or  andrcecium, 
consisting  of  a  few  or  many  parts  (stamens);  (2)  the  inner  set, 
the  gyncecium,  consisting  of  a  few  or  many  parts  (carpels). 

419 


42O  RELATION   TO   ENVIRONMENT. 

805.  Purpose  of  the  flower. — While  the  ultimate  purpose  of  all 
plants  is  the  production  of  seed  or  its  equivalent  through  which 
the  plant  gains  distribution  and  perpetuation,  the  flower  is  the 
specialized  part  of  the  seed  plant  which  utilizes  the  food  and 
energies  contributed  by  other  members  of  the  plant  organization 
for  the  production  of  seed.     In  addition  to  this  there  are  definite 
functions  performed  by  the  members  of  the  flower,  which  come 
under  the  general  head  of  plant  work,  or  flower  work. 

806.  The  calyx,  or  the  sepals.— These  are  chiefly  protective, 
affording  protection  to  the  young  stamens  and  carpels  in  the 
flower  bud.     Where  the   corolla  is  absent,   sepals  are  usually 
present  and  then  assume  the  function  of  the  petals.     In  a  few 
instances  the  calyx  may  possibly  ultimately  join  in  the  formation 
of  the  fruit  (examples:  the  butternut,  walnut,  hickory). 

807.  The  corolla,  or  petals.— The  petals  are  partly  protective 
in  the  bud,  but  their  chief  function  where  well  developed  seems 
to  be  that  of  attracting  insects,  which  through  their  visits  to  the 
flower  aid  in  "pollination"  especially  "cross  pollination" 

808.  The  stamens. — The   stamens   (  =  microsporophylls)   are 
flower   organs   for   the   production   of   pollen,   or  pollen-spores 
(  =  microspores).     The  stalk  (not  always  present)  is  the  filament, 
the  anther  is  borne  on  the  filament  when  the  latter  is  present^ 
The  anther  consists  of  the  anther  sacs  or  pollen  sacs  (microspo- 
rangium)   containing  the  pollen-spores,  and  the  connective,  the 
sterile  tissue  lying  between  and  supporting  the  anther  sac.    The 
stamens  are  usually  separate,  but  sometimes  they  are  united  by 
their  filaments,  or  by  their  anthers.    When  the  pollen  is  ripe 
they  open  by  slits  or  pores  and  the  pollen  is  scattered;   or  in 
rarer  cases  the  pollen  mass  (pollinium)  is  removed  through  the 
agency  of  insects  (see  Insect  pollination,  Chap.  XLIII). 

809.  The  pistil.— The  pistil  consists  of  the  "ovary,"  the  style 
(not  always  present),  and  the  stigma.    These  are  well  shown  in 
a  simple  pistil,  common  examples  of  which  are  found  in  the 
buttercup,   marsh   marigold,   the  pea,   bean,   etc.     The   simple 
pistil  is  equivalent  to  a  carpel  (  =  macrosporophyll),  while  the 
compound  pistil  consists  of  two  or  several  carpels  joined,  as  in 


THE  FLORAL   SHOOT.  421 

the  toothwort,  trillium,  lily,  etc.  The  ovary  is  the  enlarged  part 
which  below  is  attached  to  the  receptacle  of  the  flower,  and  con- 
tains within  the  ovules.  The  style,  when  present,  is  a  slender 
elongation  of  the  upper  end  of  the  ovary.  The  stigma  is  sup- 
ported on  the  end  of  the  style  when  the  latter  is  present.  It  is 
often  on  a  capitate  enlargement  of  the  style  or  extends  down  one 
side,  or  when  the  style  is  absent  it  is  usually  seated  directly  on 
the  upper  end  of  the  ovary.  The  stigmatic  surface  is  glutinous 
or  "sticky,"  and  serves  to  hold  the  pollen-spores  when  they 
come  in  contact  with  it. 

The  ovules  are  within  the  ovary  and  are  arranged  in  different 
ways  in  different  plants.  The  pollen-grain  (or  better  pollen- 
spore  =microspore),  after  it  has  been  transferred  to  the  stigma, 
"germinates,"  and  the  pollen  tube  grows  down  through  the 
tissue  of  the  stigma  and  style,  or  courses  down  the  stylar  canal 
until  it  reaches  the  ovule.  Here  it  usually  enters  the  ovule 
(macrosporangium)  at  the  micropyle  (in  some  of  the  ament- 
bearing  plants  it  enters  at  the  chalaza),  and  the  sperm-cells  are 
emptied  into  the  embryo  sac  in  the  interior  of  the  ovule. 

810.  Fertilization. — One  of  the  sperms  unites  with  the  egg  in 
the  embryo  -sac.     This  is  fertilization,  and  from  the  fertilized 
egg  the  young  embryo  is  formed  still  within  the  ovule.     Double 
fertilization, — the  other  sperm-cell  sometimes  unites   with  one 
or  both  of  the  "polar"  nuclei  which  have  united  to  form  the 
"definitive"  or  "endosperm"  nucleus.     A3  a  result  of  fertiliza- 
tion, the  embryo  plant  is  formed  within  the  ovule,  the  coats  of 
which  enlarge  by  growth  forming  the  seed  coats,  and  altogether 
forming  the  seed.     (See  Chapters  XXXIV,  XXXV,  XXXVI.) 

II.  Kinds  of  Flowers. 

811.  Absence  of  certain  flower  parts.— The  complete  flower 
contains  all  the  four  series  of  parts.     When  any  one  of  the  series 
of  parts  is  lacking,  the  flower  is  said  to  be  incomplete.     Where  only 
one  series  of  the  floral  envelopes  is  present  the  flowers  are  said  to 
be  apetalous   (the  petals  are  absent),  examples:  elm,  buckwheat, 


422  RELATION    TO  ENVIRONMENT. 

etc.  Flowers  which  lack  both  floral  envelopes  are  naked.  When 
pistils  are  absent  but  stamens  are  present  the  flowers  are  stami- 
nate,  whether  floral  envelopes  are  present  or  not;  and  so  when 
stamens  are  absent  and  pistils  pre  ent  the  flower  is  pistillate.  li 
both  stamens  and  pistils  are  absent  the  flower  is  said  to  be  sterile 
or  neutral  (snowball,  marginal  or  showy  flowers  in  hydrangea). 
Flowers  with  both  stamens  and  pistils,  whether  or  not  they  have 
floral  envelopes,  are  perfect  (or  hermaphrodite),  so  if  only  one 
of  these  sets  of  essential  organs  of  the  flower  is  present  the  flower 
is  imperfect,  or  diclinous.  Sometimes  the  imperfect,  or  diclinous, 
flowers  are  on  the  same  plant,  and  the  plant  is  said  to  be  monoe- 
cious (of  one  household).  When  staminate  flowers  are  on  cer- 
tain individual  plants,  and  the  pistillate  flowers  of  the  same 
species  are  on  other  individuals,  the  plant  is  dioecious  (or  of  two 
households).  When  some  of  the  flowers  of  a  plant  are  diclinous 
and  others  are  perfect,  they  are  said  to  be  polygamous. 

Many  of  these  variations  relating  to  the  presence  or  absence  of 
flower  parts  in  one  way  or  another  contribute  to  the  well-being 
of  the  plant.  Some  indicate  a  division  of  labor;  thus  in  the 
neutral  flowers  of  certain  species  of  hydrangea  or  viburnum,  the 
showy  petals  serve  to  attract  insects  which  aid  in  the  pollination 
of  the  fertile  flowers.  It  must  not  be  understood,  however,  that  all 
variations  in  plants  which  results  in  new  or  different  forms  of  flowers 
is  for  the  good  of  the  species.  For  example,  under  cultivation 
the  flowers  of  viburnum  and  hydrangea  sometimes  are  all  neu- 
tral and  showy.  While  such  variations  sometimes  contribute  to 
the  happiness  of  man,  the  plant  has  lost  the  power  of  developing 
seed.  In  diclinous  flowers  cross  pollination  is  necessitated. 

812.  Form  of  the  flower. — The  flower  as  a  whole  has  form. 
This  is  so  characteristic  that  in  general  all  flowers  of  the  different 
individuals  of  a  species  are  of  the  same  shape,  though  they  may 
vary  in  size.  In  general,  flowers  of  closely  related  plants  of  dif- 
ferent species  are  of  the  same  type  as  to  form,  so  that  often  in  the 
shape  of  the  flower  alone  we  can  see  the  relationship  of  kind, 
though  the  form  of  the  flower  is  not  the  most  important  nor 
always  the  sure  index  of  kinship.  Since  many  flowers  resemble 


THE  FLORAL  SHOOT.  423 

certain  familiar  objects,  names  are  often  used  which  relate  to 
these  objects. 

Flowers  are  said  to  be  regular,  or  irregular.  In  a  regular 
flower  all  of  the  parts  of  a  set  or  series  are  of  the  same  shape  and 
size,  while  in  irregular  flowers  the  parts  are  of  a  different  shape 
or  size  in  some  of  the  sets.  The  flowers  of  the  pea  family  (Papi- 
lionacece),  of  the  mint  family  (Labiatce),  of  the  morning  glory, 
larkspur,  monkshood,  etc.,  are  irregular  (fig.  450).  The  corolla 
usually  gives  the  characteristic  form  to  the  flower,  and  the  name 
is  usually  applied  to  the  form  of  the  corolla. 

Some  of  the  different  forms  are  wheel-shaped  or  rotate  corolla 
when  the  petals  spread  out  at  once  like  the  spokes  of  a  wheel,  as 
in  the  potato,  tomato,  or  bittersweet;  salver-shaped  when  the 


Fig.  450. 

Several  forms  of  flowers.  Regular  flowers,  wh,  wheel-shaped  corolla;  sa, 
salver-shaped;  tub,  tubular-shaped.  Irregular  flowers,  pa,  butterfly  or  papilio- 
naceous; per,  personate  or  masked  flower;  lab,  gaping  or  ringent  corolla.  The 
two  latter  are  called  bilabiate  flowers. 

petals  spread  out  at  right  angles  from  the  end  of  a  corolla  tube, 
as  in  the  phlox;  bell-shaped,  or  campanulate,  as  in  the  harebell 
or  campanula;  funnel-shaped,  as  in  the  morning  glory;  tubular, 
when  the  ends  of  the  petals  spread  but  little  or  none  from  the 
end  of  the  corolla  tube,  as  in  the  turnip  flower  or  in  the  disk 
florets  of  the  composites.  The  butterfly,  or  papilionaceous  cor- 
olla is  peculiar  as  in  the  pea  or  bean.  The  upper  petal  is  the 
"banner,"  the  two  lateral  ones  the  "wings,"  and  the  two  lower 
the  "keel." 

The  labiate  corolla  is  charcteristic  of  the  mint  family  where 
the  gamosepalous  corolla  is  unequally  divided,  so  that  the  two 


424  RELATION   TO   ENVIRONMENT. 

upper  lobes  are  sharply  separated  from  the  three  lower  forming 
two  "lips."  The  labiate  corolla  of  the  toadflax,  or  snapdragon 
is  personate,  or  masked,  because  the  lower  lip  arches  upward 
like  a  palate  and  closes  the  entrance  to  the  corolla  tube;  that  of 
the  dead  nettle  (Lamium)  is  ringent  or  gaping,  because  the  lips 
are  spread  wide  apart.  In  some  plants  the  labiate  corolla  is  not 
very  marked  and  differs  but  slightly  from  a  regular  form. 

The  llgulate  or  strap-shaped  corolla  is  characteristic  of  the 
flowers  of  the  dandelion  or  chicory,  or  of  the  ray  flowers  of  other 
composites  (fig.  451).  The  lower  part  of  the  gamosepalous 
corolla  is  tubular,  and  the  upper  part  is  strap-shaped,  as  if  that 
part  of  the  tube  were  split  on  one  side  and  spread  out  flat. 

These  forms  of  the  flower  should  be  studied  in  appropriate 
examples  in  connection  with  flower  types  and  relations  in  Chap- 
ters LVIII-LXV. 

813.  Union  of  flower  parts. — In  the  buttercup  flower  all  the 
parts  of  each  series  are  separate  from  one  another  and  from 
other  series  of  parts.     Each  one  is  attached  to  the  receptacle  of 
the  flower,  which  is  a  very  much  shortened  portion  of  the  flower 
axis.     The  calyx  being  composed  of  separate  and  distinct  parts 
is  said  to  be  polysepalous,  and  the  corolla  is  likewise  polypetal- 
ous.     The  stamens  are  distinct,  and  the  pistils  are  simple.     In 
many  flowers,  however,  there  is  a  greater  or  lesser  union  of  parts. 

814.  Union  of  parts  of  the  same  series  or  cycle. — The  parts 
coalesce,  either  slightly  or  to  a  great  extent.     Usually  they  are 
not  so  completely  coalesced  but  what  the  number  of  parts  of 
the  series  can  be  determined.     Where  the  sepals  are  united  the 
calyx  is  gamosepalous,  when  the  petals  are  united  the  corolla  is 
gamopetalous  (Chapter  LXV). 

Union  of  the  sepals  or  of  the  corolla  is  quite  common,  but 
union  of  the  stamens  is  rare  except  in  a  few  families  where 
it  is  quite  characteristic.  When  the  stamens  are  united  by 
their  anthers,  they  are  syngencesious.  This  is  the  case  in 
most  flowers  of  the  composite  family.  When  all  the  stamens 
are  united  into  one  group  by  their  filaments,  they  are  mona- 
delphous  (one  brotherhood),  as  in  holyhock,  hibiscus,  cotton, 


THE  FLORAL    SHOOT.  425 

marsh-mallow,  etc.  When  they  are  united  by  their  filaments  in 
two  groups,  they  are  diadelphous  (two  brotherhoods),  as  in  the 
pea  and  most  members  of  the  pea  family.  In  most  species  of 
St.  John's  wort  (Hypericum),  the  stamens  are  united  in  threes 
(triadelphous) . 

815.  The  carpels  are  often  united. — The  pistil  is  then  said  to 
be  compound.     Where  the  carpels  are  consolidated,  usually  the 
adjacent  walls  coalesce  and  thus  separate  the  cavity  of  each 
ovary.     Each   cavity  in   the   compound   pistil  is   a   locule.     In 
some  cases  the  adjacent  walls  disappear  so  that  there  is  one  com- 
mon cavity  for  the  compound  pistil  (examples:  purslane,  chick- 
weeds,  pinks,  etc.).     In  a  few  cases  there  is  a  false  partition 
(example,  in  the  toothwort  and  other  crucifers).     The  compound 
pistil  is  very  often  lobed  slightly,  so  that  the  different  carpels  can 
be  discerned.     More  often  the  styles  or  stigmas  are  distinct,  and 
thus  indicate  the  number  of  carpels  united. 

816.  Union  of  the  parts  of  different  series. — While  in  the 
buttercup  and  many  other  flowers,  all  the  different  parts  are 
inserted  on  the  torus  or  receptacle,  in  other  flowers  one  series  of 
parts  may  be  joined  to  another.     This  is  adnation  of  parts,  or 
the  two  or  more  series  are  adnate.     In  the  morning  glory  the 
stamens  are  inserted  on  the  inner  face  of  the  corolla  tube;    the 
same  is  true  in  the  mint  family,  and  there  are  many  other  ex- 
amples.    The  insertion  of  parts,  whether  free  or  adnate,  is  usually 
spoken  of  in  reference  to  their  relation  to  the  pistil.     Thus, 
in  the  buttercup  the  floral  envelopes  and  stamens  are  all  free 
and  hypogenous,  they  are  below  the  pistil  (Chapter  LXII).     The 
pistil  in  this  case  is  superior.     In  the  cherry,  pear,  etc.,  the  petals 
and  stamens  are  borne  on  the  edge  of  the  more  or  less  elevated 
tube  of  the  calyx,  and  are  said  to  be  perigynous,  i.e.,  around  the 
pistil  (fig.  565).     In  the  cranberry,  huckleberry,  etc.,  the  calyx 
is  for  the  most  part  united  with  the  wall  of  the  ovary  with  the 
short    calyx    limbs    projecting    from    the    upper    surface.     The 
petals  and  stamens  are  inserted  on  the  edge  of  the  calyx  above 
the  ovary;    they  are,  therefore,  epigynous,  and  the  ovary  being 
under  the  calyx,  as  it  were,  is  inferior  (fig.  576). 


426  RELATION   TO  ENVIRONMENT. 


III.  Arrangement  of  Flowers,  or  Mode  of  Inflores- 
cence. 

817.  Flowers  are  solitary  or  clustered. — Solitary  flowers  are 
more  simple  in  their  arrangement,  i.e.,  it  is  easier  for  us  to  deter- 
mine and  name  their  relation  to  each  other  and  to  other  parts 
of  the  plant.  They  are  either  axillary,  i.e.,  on  short  lateral 
shoots  in  the  axils  of  ordinary  foliage  leaves,  or  they  are  terminal, 
i.e.,  they  are  borne  on  the  end  of  the  main  axis  of  an  ordinary 
foliage  shoot.  In  either  case  they  are  so  far  separated,  and  the 
foliage  leaves  are  so  prominent,  they  do  not  form  recognizable 
groups  or  clusters.  The  manner  of  arrangement  of  flowers  on 
the  shoot  is  called  inflorescence,  while  the  group  of  flowers  so 
arranged  is  the  flower  cluster. 

Two  different  modes  of  inflorescence  are  usually  recognized 
in  the  arrangement  of  flowers  on  the  stem,  (i)  The  corymbose, 
or  indeterminate  inflorescence  (also  indefinite  inflorescence),  in 
which  the  flowers  arise  from  axillary  buds,  and  the  terminal  bud 
may  continue  to  grow.  (2)  The  cymose  or  determinate  inflor- 
escence (also  definite  inflorescence)  in  which  the  flowers  arise 
from  terminal  buds.  This  arrests  the  growth  of  the  shoot  in 
length. 

There  are  several  advantages  to  the  plant  in  the  different 
modes  of  inflorescence,  chief  among  which  is  the  massing  of  the 
flowers,  thus  increasing  the  chances  for  effective  pollination. 

A.  FLOWER   CLUSTERS   WITH   INDETERMINATE    INFLORESCENCE. 

818.  The  simplest  mode  of  indeterminate  inflorescence  is 

where  the  flowers  arise  in  the  axils  of  normal  foliage  leaves, 
while  the  terminal  bud,  as  in  the  florist's  smilax,  the  bellwort, 
moneywort,  apricot,  etc.,  continues  to  grow.  The  flowers  are 
solitary  and  axillary.  In  other  cases  which  are  far  more  numer- 
ous, the  flowers  are  associated  into  more  or  less  definite  clusters 
in  which  are  a  number  of  recognizable  types.  The  word  type 
used  in  this  sense,  it  should  be  understood,  does  not  refer  to  an 


THE  FLORAL   SHOOT.  427 

original  structure  which  is  the  source  of  others.  It  merely  refers 
to  a  mode  of  inflorescence  which  we  attempt  to  recognize,  and 
about  which  we  group  those  forms  which  have  a  resemblance  to 
one  another.  There  are  many  forms  of  flower  clusters  which 
do  not  conform  to  any  one  of  our  recognized  types,  and  are  very 
puzzling.  The  evolution  of  the  flower  clusters  has  been  natural, 
and  we  cannot  make  them  all  conform  to  an  artificial  classifica- 
tion. These  types  are  named  merely  as  a  matter  of  convenience 
in  the  expression  of  our  ideas.  The  types  usually  recognized 
are  as  follows: 

819.  The  raceme. — The  flower-shoot  is  more  or  less  elongated, 
and  the  leaves  are  reduced  to  a  minute  size  termed  bracts,  while 
the  flowers  on  lateral  axes  are  solitary  in  the  axils  of  the  bracts. 
The  reduction  in  the  size  of  the  leaves  and  the  somewhat  limited 
growth  of  the  shoot  in  length,  makes  the  flowers  more  prominent, 
and  brings  them  into  closer  relation  than  if  they  were  formed  in 
the  axils  of  the  leaves  on  the  ordinary  foliage  shoot.     The  choke 
cherry,   currant,  pokeweed,   sourwood,  etc.,  are  examples  of  a 
raceme  (fig.  569).     In  most  plants  with  the  raceme  type,  while 
the  inflorescence  is  indeterminate,  and  the  uppermost  flowers 
(those  toward  the  end  of  the  main  shoot)  are  younger,  still  the 
period  of  flowering  is  somewhat  restricted  and  the  raceme  stops 
growing.     In  a  few  plants,  however,  as  in  the  common  "shep- 
herd's purse,"   the   raceme   continues  to  grow   throughout    the 
summer,  so  that  the  lower  flowers  may  have  ripened  their  seed 
while  the  terminal  portion  of  the  raceme  is  still  growing  and 
producing  new  flowers.     Compound  racemes  are  formed  when 
by  branching  of  the  flower-shoot  there  are  several  racemes  in  a 
cluster,  as  in  the  false  Solomon's  seal  (Smilacina  racemosa). 

820.  The  panicle. — The  panicle  is  developed  from  the  raceme 
type  by  the  branching  of  the  lateral  flower-axes  forming  a  loose 
open  flower  cluster,  as  in  the  oat. 

821.  The  thyrsus  is  a  compact  panicle  of  pyramidal  form,  as 
in  the  lilac,  horsechestnut,  etc. 

822.  The  corymb. — The  corymb  shows  likewise  an  easy  tran- 
sition from  the  raceme  type,  by  the  shortening  of  the  main  axis 


428  RELATION    TO  ENVIRONMENT. 

of  inflorescence,  and  the  lengthening  of  the  lower,  lateral  flower 
peduncles  so  that  the  flower  cluster  is  more  or  less  flattened  on 
top.  This  represents  the  simple  corymb.  A  compound  corymb 
ls  one  in  which  some  of  the  flower  peduncles  branch  again  form- 
ing secondary  corymbs,  as  in  the  mountain  ash.  It  is  like  a 
panicle  with  the  lower  flower  stalks  elongated. 

823.  The  umbel.— The  umbel  is  developed  from  the  raceme, 
or  corymb.     The  main  flower-shoot  remains  very  short  or  unde- 
veloped with  several  flowers  on  long  peduncles  arising  close  to- 
gether around  this  shortened  axis,  in  the  form  of  a  whorl  or  clus- 
ter.    Examples  are  found  in  the  milkweed,   water  pennywort 
(Hydrocotyle),  the  oxheart  cherry,  etc.     A  compound  umbel  is 
one  in  which  the  peduncles  are  branched,  forming  secondary 
umbels,  as  in  the  caraway,  parsnip,  carrot,  etc.  (figs.  578,  579). 

824.  The  spike. — In  the  spike  the  main  axis  is  long,  and  the 
solitary  flowers  in  the  axils  of  the  bracts  are  usually  sessile,  and 
often  very  much  crowded.     The  plaintain,  mullein   (fig.  422), 
etc.,  are  examples.     The  spike  is  a  raceme,  only  the  flowers  are 
sessile  and  crowded.     In  the  grasses  the  flower  cluster  is  branched, 
and  the  branchlets  bearing  a  few  flowers  are  spikelets. 

825.  The  head.— When  the  flower  axis  is  very  much  short- 
ened and  the  flowers  crowded  and  sessile  or  nearly  so,  forming  a 
globose  or  compressed  cluster,  it  is  a  head  or  capitulum.    The 
transition  is  from  a  spike  by  the  shortening  of  the  main  axis,  as 
in  the  clover,  button  bush  (Cephalanthus),  etc.,  or  in  the  short- 
ening of  the  peduncles  in  an  umbel,  as  in  the  daisy,  dandelion, 
and  other  composite  flowers.     In  these  the  head  is  surrounded 
by  an  involucre,  which  in  the  young  head  often  envelopes  the 
mass  of  flowers,  thus  affording  them  protection.     In  some  other 
composites   (Lactuca,   for  example)   the  involucre  affords  pro- 
tection for  a  longer  period,  even  while  the  seeds  are  ripening. 

826.  The  spadix. — When  the  main  axis  of  the  flower  cluster 
is  fleshy,  the  spike  or  head  forms  a  spadix,  as- in  the  Indian  tur- 
nip, the  skunk  cabbage,  the  calla,  etc.     The  spadix  is  usually 
more  or  less  enclosed  in  a  spathe,  a  somewhat  strap-shaped  leaf. 

827.  The  catkin. — A  spike  which  is  usually  caducous,  i.e., 


THE  FLORAL   SHOOT.  429 

falls  away  after  the  maturity  of  the  flower  or  fruit,  is  called  a 
catkin,  or  an  ament.  The  flower  clusters  of  the  alder,  willow, 
(fig.  555),  poplar,  and  the  staminate  flower  clusters  of  the  oak, 
hickory,  hazel,  birch,  etc.,  are  aments.  So  characteristic  is  this 


Fig.  451. 

Head  of  sunflower  showing  centripetal  inflorescence  of  tubular  flowers.  (Photo 
by  the  Author.) 

mode  of  inflorescence  that  the  plants  are  called  amentijerous,  or 
amentaceous. 

828.  Anthesis  of  flowers  with  indeterminate  inflorescence. — 
In  the  anthesis  of  the  raceme  as  well  as  in  other  corymbose  forms 
the  lower  (or  outer)  flowers  being  older,  open  first.  The  open- 
ing of  the  flowers  then  takes  place  from  below,  upward;  or  from 
the  outside,  inward  toward  the  center  of  inflorescence.  The 
anthesis,  i.e.,  the  opening  of  the  flowers  of  corymbose  forms  is 
said  to  be  centripetal,  i.e.,  it  progresses  from  outside,  inward. 
The  anthesis  of  the  fuller's  teazel  is  peculiar,  since  it  shows  both 
types.  There  are  several  distinct  advantages  to  the  plant  where 


430 


RELATION   TO  ENVIRONMENT. 


anthesis  extends  over  a  period  of  time,  as  it  favors  cross  pollina- 
tion, favors  the  formation  of  seed  in  case  conditions  should  be 


Fig.  452. 
Heads  of  fuller's  teazel  in  different  stages  of  flowering. 

unfavorable  at  one  period  of  anthesis,  distributes  the  drain  on 
the  plant  for  food,  etc. 

B.  FLOWER  CLUSTERS  WITH  DETERMINATE  INFLORESCENCE. 

829.  The  simplest  mode  of  determinate  inflorescence  is  a 
plant  with  a  solitary  terminal  flower,  as  in  the  hepatica,  the  tulip, 
etc.     The  leaves  in  these  two  plants  are  clustered  in  the  form  of  a 
rosette,  and  the  aerial  shoot  is  naked  and  bears  the  single  flower 
at  its  summit.     Such  a  flower-shoot  is  a  scape.     As  in  the  case 
of  the    indeterminate  inflorescence,  so  here  the  larger  number 
of  flower-shoots  are  more  complex  and  specialized,  resulting  in 
the  evolution  of  flower  clusters  or  masses.     Accompanying  the 
association  of  flowers  into  clusters  there  has  been  a  reduction  in 
leaf  surface  on  the  flower-shoot  so  that  the  flowers  predominate 
in   mass   and   are   more   conspicuous.     Among   the   recognized 
modes  of  determinate  inflorescence,  the  following  are  the  chief 
ones: 

830.  The  cyme. — In  the  cyme  the  terminal  flower  on  the  main 
axis  opens  first  and  the  remaining  flowers  are  borne  on  lateral 
shoots,  which  arise  from  the  axils  of  leaves  or  bracts,  below 


THE  FLORAL    SHOOT. 


431 


These  lateral  shoots  usually  branch  and  elongate  so  that  the 
terminal  flowers  on  all  the  branches  reach  nearly  the  same  height 
as  the  terminal  flower  on  the  main  shoot,  forming  a  somewhat 
flattened  or  convex  top  of  the  flower  cluster.  This  is  illustrated 


A  S     £  0 

Fig.  453- 

Diagrams  of  cymose  inflorescence.     A,  dichasium;    B,  scorpioid  cyme;    C,  heli- 
coid  cyme.     (After  Strasburger. ) 

in  the  basswood  flower.  The  anthesis  of  the  cyme  is  centrifugal, 
i.e.,  from  the  inside  outward  to  the  margin.  But  it  is  often  more 
or  less  mixed,  since  the  lateral  shoots  if  they  bear  more  than  one 
flower  are  dimunitive  cymes  and  the  terminal  flower  opens  before 
the  lateral  ones.  Where  the  flower  cluster  is  quite  large  and 
the  branching  quite  extensive,  compound  cymes  are  formed,  as 
in  the  dogwood,  hydrangea,  etc. 

831.  The   helicoid  cyme. — Where  successive  lateral  branch- 
ing takes  place,  and  always  continues  on  the  same  side  a  curved 
flower  cluster  is  formed,  as  in  the  forget-me-not  and  most  mem- 
bers of  the  borage  family.     This  is  known  as  a  helicoid  cyme 
(fig.  453,  Q-     Each  new  branch  becomes  in  turn  the  "false" 
axis  bearing  a  new  branch  on  the  same  side. 

832.  The  scorpioid  cyme. — A  scorpioid  cyme  (fig.  453,  B)  is 
formed  where  each  new  branch  arises  on  alternate  sides  of  the 
"false"  axis. 

833.  The  forking  cyme  is  where  each  "false"  axis  produces 
two  branches  opposite,  so  that  it  represents  a  false  dichotomy 
(example,  the  flower  cluster  of  chickweed). 

834.  Some  of  these  flower  clusters  are  peculiar  and  it  is  dim- 


432  RELATION   TO  ENVIRONMENT. 

cult  to  see  how  the  helicoid,  or  scorpioid,  cymes  are  of  any 
advantage  to  the  plant  over  a  true  cyme.  The  inflorescence  of 
the  plant  being  determinate,  if  the  flowering  is  to  be  extended 
over  a  considerable  period  a  peculiar  form  would  necessarily 
result.  In  the  helicoid  cyme  continued  branching  takes  place 
on  one  side,  and  the  result  in  the  forget-me-not  is  a  continued 
inflorescence  in  its  effect  like  that  of  a  continued  raceme  (com- 
pare shepherd's-purse).  But  we  should  not  expect  that  all 
of  the  complex  and  specialized  structures  from  simple  and  gen- 
eralized ones  are  beneficial  to  the  plant.  In  many  plants  we 
recognize  evolution  in  the  direction  of  advantageous  structures. 
But  since  the  plant  cannot  consciously  evolve  these  structures, 
we  must  also  recognize  that  there  may  be  phases  of  retrogression 
in  which  the  structures  evolved  are  not  so  beneficial  to  the  plant 
as  the  more  simple  and  generalized  ones  of  its  ancestors.  Varia- 
tion and  change  do  not  result  in  advancing  the  plant  or  plant 
structures  merely  along  the  lines  which  will  be  beneficial.  The 
tendency  is  in  all  directions.  The  result  in  general  may  be  dia- 
gramed by  a  tree  with  divergent  and  wide-reaching  branches. 
Some  die  out;  others  remain  subordinate  or  dormant;  while 
still  others  droop  downward,  showing  a  retrogression.  But  in 
this  backward  evolution  they  do  not  return  to  the  condition  of 
their  ancestors,  nor  is  the  same  course  retraced.  A  new  down- 
ward course  is  followed  just  as  the  downward-growing  branch 
follows  a  course  of  its  own,  and  does  not  return  in  the  trunk. 


CHAPTER  XLIII. 

POLLINATION. 

Origin  of  heterospory,  and  the  necessity  for 
pollination. 

835.  Both  kind*-,  of  sexual  organs  on  the  same  prothallium. — In  the  ferns,  as 
we  have  seen,  the  sexual  organs  are  borne  on  the  prothallium,  a  small,  leaf-like, 
heart-shaped  body  growing  in  moist  situations.     In  a  great  many  cases  both 
kinds  of  sexual  organs  are  borne  on  the  same  prothallium.     While  it  is  per- 
haps riot  uncommon,  in  some  species,  that  the  egg  cell  in  an  archegonium 
may  be  fertilized  by  a  spermatozoid  from  an  antheridium  on  the  same  pro- 
thallium,  it  happens  many  times  that  it  is  fertilized  by  a  spermatozoid  from 
another  prothallium.     This  may  be  accomplished  in  several  ways.     In  the 
first  place  antheridia  are  usually  found  much  earlier  on  the  prothallium  than 
are  the  archegonia.     When  these  antheridia  are  ripe,  the  spermatozoids  es- 
cape before  the  archegonia  on  the  same  prothallium  are  mature. 

836.  Cross  fertilization  in  monoecious  prothallia. — By  swimming  about  in 
the  water  or  drops  of  moisture  which  are  at  times  present  in  these  moist  situa- 
tions,  these  spermatozoids  may  reach  and  fertilize  an  egg  which   is  ripe 
in  an  archegonium  borne  on  another  and  older  prothallium.     In  this  way 
what  is  termed  cross  fertilization  is  brought  about  nearly  as  effectually  as  if 
the  prothallia  were  dioecious,  i.e.  if  the  antheridia  and  archegonia  were  all 
borne  on  separate  prothallia. 

837.  Tendency  toward  dioecious  prothallia. — In  other  cases  some  fern  pro- 
thallia bear  chiefly  archegonia,  while  others  bear  only  antheridia.     In  these 
cases  cross  fertilization  is  enforced  because  of  this  separation  of  the  sexual 
organs  on  different  prothallia.      These  different  prothallia,   the  male  and 
female,  are  largely  due  to  a  difference  in  food  supply,  as  has  been  clearly 
proven  by  experiment. 

838.  The  two  kinds  of  sexual  organs  on  different  prothallia. — In  the  horse- 
tails (equisetum)  the  separation  of  the  sexual  organs  on  different  prothallia  has 
become  quite  constant.     Although  all  the  spores  are  alike,  so  far  as  we  can 
determine,  some  produce  small  male  plants  exclusively,  while  others  produce 

433 


434  RELATION-    TO  ENVIRONMENT. 

large  female  plants,  though  in  some  cases  the  latter  bear  also  antheridia.  It 
has  been  found  that  when  the  spores  are  given  but  little  nutriment  they  form 
male  prothallia,  and  the  spores  supplied  with  abundant  nutriment  form 
female  prothallia. 

839.  Permanent  separation  of  sexes  by  different  amounts  of  nutriment  sup- 
plied the  spores. — This  separation  of  the  sexual  organs  of  different  prothallia, 
which  in  most  of  the  ferns,  and  in  equisetum,  is  dependent  on  the  chance 
supply  of  nutriment  to  the  germinating  spores,  is  made  certain  when  we  come 
to  such  plants  as  isoetes  and  selaginella.     Here  certain  of  the  spores  receive 
more  nutriment  while  they  are  forming  than  others.     In  the  large  sporangia 
(macrosporangia)  only  a  few  of  the  cells  of  the  spore-producing  tissue  form 
spores,  the  remaining  cells  being  dissolved  to  nourish  the  growing  macro- 
spores,  which  are  few  in  number.     In  the  small  sporangia  (microsporangia) 
all  the  cells  of  the  spore-producing  tissue  form  spores.     Consequently  each 
one  has  a  less  amount  of  nutriment,  and  it  is  very  much  smaller,  a  micro- 
spore.     The  sexual  nature  of  the  prothallium  in  selaginella  and  isoetes,  then,  is 
predetermined  in  the  spores  while  they  are  forming  on  the  sporophyte.     The 
microspores  are  to  produce  male  prothallia,  while  the  macrospores  are  to 
produce  female  prothallia. 

840.  Heterospory. — This   production  of  two  kinds  of  spores  by  isoetes, 
selaginella,  and  some  of  the  other  fern  plants    is  heterospory,  or  such  plants 
are  said  to  be  heterosporous.    Heterospory,  then,  so  far  as  we  know  from  liv- 
ing forms,  has  originated  in  the  fern  group.     In  all  the  higher  plants,  in  the 
gymnosperms  and  angiosperms,  it  has  been  perpetuated,  the  microspores  being 
represented  by  the  pollen,  while  the  macrospores  are  represented  by  the  em- 
bryo sac;  the  male  organ  of  the  gymnosperms  and  angiosperms  being  the 
antherid  cell  in  the  pollen  or  pollen  tube,  or  in  some  cases  perhaps  the  pollen 
grain  itself,   and  the  female  organ  in  the  angiosperms  perhaps  reduced  to 
the  egg  cell  of  the  embryo  sac. 

841.  In  the  pteridophytes  water  serves  as  the  medium  for  conveying  the 
sperm  cell  to  the  female  organ. — In  the  ferns  and  their  allies,  as  well  as  in 
the  liverworts  and  mosses,   surface   water  is  a  necessary  medium   through 
which  the  generative  or  sperm  cell  of  the  male  organ,  the  spermatozoid,  may 
reach  the  germ  cell  of  the  female  organ.     The  sperm  cell  is  here  motile. 
This  is  true  in  a  large  number  of  cases  in  the  algae,  which  are  mostly  aquatic 
plants,  while  in  other  cases  currents  of  water  float  the  sperm  cell  to  the 
female  organ. 

842.  In  the  higher  plants  a  modification  of  the  prothallium  is  necessary. 
— As  we  pass  to  the   gymnosperms  and  angiosperms,  however,  where  the 
primitive  phase  (the  gametophyte)  of  the  plants  has  become  dependent  solely 
on  the  modern  phase  (the  sporophyte)  of  the  plant,  surface  water  no  longer 
serves  as  the  medium  through  which  a  motile  sperm  cell  reaches  the  egg  cell 
to  fertilize  it     The  female  prothallium,  or  macrospore,  is,  in   nearly  alJ 


POLLINATION.  435 

cases,  permanently  enclosed  within  the  sporangium,  so  that  if  there  were 
motile  sperm  cells  on  the  outside  of  the  ovary,  they  could  never  reach  the 
egg  to  fertilize  it. 

843.  But  a  modification  of  the  microspore,  the   pollen  tube,  enables  the 
sperm  cell  to   reach  the  egg  cell.     The  tube  grows  through  the  nucellus, 
or  first  through  the  tissues  of  the  ovary,  deriving  nutriment  therefrom. 

844,  But  here  an  important  consideration  should  not  escape  us.     The  pol- 
len grains  (microspores)  must  in  nearly  all  cases  first  reach  the  pistil,  in 
order  that  in  the  growth  of  this  tube  a  channel  may  be  formed  through  which 
the  generative  cell  can  make  its  way  to  the  egg  cell.     The  pollen  passes  from 
the  anther  locule,  then,  to  the  stigma  of  the  ovary.     This  process  is  termed 
pollination. 


Pollination. 

845.  Self  pollination,  or  close  pollination.— Perhaps  very  few  of  the  ad- 
mirers of  the  pretty  blue  violet  have  ever  noticed  that  there  are  other  flowers 
than   those  which  appeal  to  us  through  the  beautiful  colors  of  the  petals. 
How  many  have  observed  that  the  brightly  colored  flowers  of  the  blue  violet 
rarely  "  set  fruit"  ?     Underneath  the  soil  or  debris  at  the  foot  of  the  plant 
are  smaller  flowers  on  shorter,  curved  stalks,  which  do  not  open.     When  the 
anthers  dehisce,  they  are  lying  close  upon  the  stigma  of  the  ovary,  and  the 
pollen  is  deposited  directly  upon  the    stigma  of  the  same  flower.      This 
method  of  pollination  is  self  pollination,  or  close  pollination.     These  small, 
closed  flowers  of  the  violet  have  been  termed  "  cleistogamous"  because  they 
are  pollinated  while   the  flower  is  closed,  and  fertilization  takes  place  as  a 
result. 

But  self  pollination  takes  place  in  the  case  of  some  open  flowers.  In  some 
cases  it  takes  place  by  chance,  and  in  other  cases  by  such  movements  of  the 
stamens,  or  of  the  flower  at  the  time  of  the  dehiscence  of  the  pollen,  that  it 
is  quite  certainly  deposited  upon  the  stigma  of  the  same  flower. 

846.  Wind  pollination. — The  pine  is  an  example  of  wind-pollinated  flowers. 
Since  the  pollen  floats  in  the  air  or  is  carried  by  the  "wind,"  such  flowers  are 
anemophilous .     Other  anemophilous  flowers  are  found  in  other  conifers,  in 
grasses,  sedges,  many  of  the    ament-bearing  trees,  and  other  dicotyledons. 
Such   plants   produce    an    abundance   of  pollen    and  always  in  the  form  of 
"dust,"  so  that  the  particles  readily  separate  and  are  borne  on  the  wind. 

847.  Pollination  by  insects. — A  large  number  of  the  plants  which  we  have 
noted    as   being  anemophilous  are  monoecious  or  dioecious,  i.  e.  the  stamens 
and  pistils  are  borne  in  separate  flowers.    The  two  kinds  of  flowers  thus  formed, 
the   male    and   the   female,  are  borne  either  on  the  same  individual  (monoe- 
cious) or  on  different  individuals  (dioecious).     In  such  cases  cross  pollination, 


436 


RELATION   TO  ENVIRONMENT. 


i.e.  the  pollination  of  the  pistil  of  one  flower  by  pollen  from  another,  is 
sure  to  take  place,  if  it  is  pollinated  at  all.  Even  in  monoecious  plants  cross 
pollination  often  takes  place  Between  flowers  of  different  individuals,  so  that 


Fig.  454- 

Viola  cucullata;  blue  flowers  above,  cleistogatnous  flowers  smaller  and  curved  below. 
Section  of  pistil  alright. 

more  widely  different  stocks  are  united  in  the  fertilized  egg,  and  the  strain 
is  kept  more  vigorous  than  if  very  close  or  identical  strains  were  united. 

848.  But  there  are  many  flowers  in  which  both  stamens  and  pistils  are  pres- 
ent, and  yet  in  which  cross  pollination  is  accomplished  through  the  agency  oJ 
insects. 

859.  Pollination  of  the  bluet. — In  the  pretty  bluet  the  stamens  and 
styles  of  the  flowers  are  of  different  length  as  shown  in  figures  455,  456. 
The  stamens  of  the  long-styled  flower  are  at  about  the  same  level  as  the 
stigma  of  the  short-styled  flower,  while  the  stamens  of  the  latter  are  on 


POLLINA  TION. 


437 


about  the  same  level  as  the  stigma  of  the  former.  What  does  this  interesting 
relation  of  the  stamens  and  pistils  in  the  two  different  flowers  mean  ?  As  the 
butterfly  thrusts  its  "tongue"  down  into  the  tube  of  the  long-styled  flower 


Fig.  45  ;• 
Dichogamous  flower  of  the  bluet  (Houstonia  coerulea),  the  long-styled  form. 

for  the  nectar,  some  of  the  pollen  will  be  rubbed  off  and  adhere  to  it.  When 
now  the  butterfly  visits  a  short-styled  flower  this  pollen  will  be  in  the  right 
position  to  be  rubbed  off  onto  the  stigma  of  the  short  style.  The  positions  of 


Fig.  456. 
Dichogamous  flower  of  bluet  (Houstonia  crerulea),  the  short-styled  form. 

the  long  stamens  and  long  style  are  such  that  a  similar  cross  pollination  will 
be  effected. 

850.  Pollination  of  ttie  primrose. — In  the  primroses,  of  which  we  have 
examples  growing  in  conservatories,  that  blossom  during  the  winter,  we 
have  almost  identical  examples  of  the  beautiful  adaptations  for  cross  polli- 
nation by  insects  found  in  the  bluet.  The  general  shape  of  the  corolla  is 


RELATION   TO   ENVIRONMENT. 

the  same,  but  the  parts  of  the  flower  are  in  fives,  instead  of  in  fours  as  in 
the  bluet.  While  the  pollen  of  the  short-styled  primulas  sometimes  must 
fall  on  the  stigma  of  the  same  flower,  Darwin  has  found  that  such  pollen  is 


Fig.  45  7- 
Dichogamous  flowers  of  primula. 

not  so  potent  on  the  stigma  of  its  own  flower  as  on  that  of  another,  an  ad- 
ditional provision  which  tends  to  necessitate  cross  pollination. 

In  the  case  of  some  varieties  of  pear  trees,  as  the  bartlett,  it  has  been 
found  that  the  flowers  remain  largely  sterile  not  only  to  their  own  pollen,  or 
pollen  of  the  flowers  on  the  same  tree,  but  to  all  flowers  of  that  variety. 
However,  they  become  fertile  if  cross  pollinated  from  a  different  variety  of 
pear. 

851.  Pollination  of  the  skunk's  cabbage. — In  many  other  flowers  cross 
pollination  is  brought  about  through  the  agency  of  insects,  where  there  is  a 
difference  in  time  of  the  maturing  of  the  stamens  and  pistils  of  the  same 
flower.  The  skunk's  cabbage  (Spathyema  foetida),  though  repulsive  on 
account  of  its  fetid  odor,  is  nevertheless  a  very  interesting  plant  to  study  for 
several  reasons.  Early  in  the  spring,  before  the  leaves  appear,  and  in  many 
cases  as  soon  as  the  frost  is  out  of  the  hard  ground,  the  hooked  beak  of  the 
large  fleshy  spathe  of  this  plant  pushes  its  way  through  the  soil. 

If  we  cut  away  one  side  of  the  spathe  as  shown  in  fig.  459  we  shall  have 
the  flowering  spadix  brought  closely  to  view.  In  this  spadix  the  pistil  of 
each  crowded  flower  has  pushed  its  style  through  between  the  plates  of 
armor  formed  by  the  converging  ends  of  the  sepals,  and  stands  out  alone 
with  the  brush-like  stigma  ready  for  pollination,  while  the  stamens  of  all  the 
flowers  of  this  spadix  are  yet  hidden  beneath.  The  insects  which  pass  from 
the  spadix  of  one  plant  to  another  will,  in  crawling  over  the  projecting 
stigmas,  rub  off  some  of  the  pollen  which  has  been  caught  while  visiting  a 
plant  where  the  stamens  are  scattering  their  pollen.  In  this  way  cross  pollin- 
ation is  brought  about.  Such  flowers,  in  which  the  stigma  is  prepared 


POLLINA  TION~. 


439 


Fig.  459.  440 

Proterogyny  in  skunk's  cabbagtt.     (Photograph  by  the  author.) 


POLLINA  TION. 


441 


Fig.  460. 
Skunk's  cabbage  •   upper  flowers  protcrandrous,  lower  ones  proterogynouc. 


442  RELATION   TO   ENVIRONMENT. 

for   pollination    before  the  anthers  of  the  same  flower  are  ripe,  are  prater- 
ogynous. 

852.  Now  if  we  observe  the  spadix  of  another  plant  we  may  see  a  condi- 
tion of  things  similar  to  that  shown  in  fig.  460.  In  the  flowers  in  the  upper 
part  of  the  spadix  here  the  anthers  are  wedging  their  way  through  between 
the  armor-like  plates  formed  by  the  sepals,  while  the  styles  of  the  same 
flowers  are  still  beneath,  and  the  stigmas  are  not  ready  for  pollination.  Such 
flowers  are  proterandrotts,  that  is,  the  anthers  are  ripe  before  the  stigmas  of 
the  same  flowers  are  ready  for  pollination.  In  this  spadix  the  upper  flowers 
are  proterandrous,  while  the  lower  ones  are  proterogynous,  so  that  it  might 
happen  here  that  the  lower  flowers  would  be  pollinated  by  the  pollen  falling 
on  them  from  the  stamens  of  the  upper  flowers.  This  would  be  cross  pol- 
lination so  far  as  the  flowers  are  concerned,  but  not  so  far  as  the  plants  are 
concerned.  In  some  individuals,  however,  we  find  all  the  flowers  proter- 
androus. 

853  Spiders  have  discovered  this  carious  relation  of  the  flowers  and  in 
sects.  —  On  several  different  occasions,  while  studying  the  adaptations  of  the 
flowers  of  the  skunk's  cabbage  for  cross  pollination,  I  was  interested  to  find 
that  the  spiders  long  ago  had  discovered  something  of  the  kind,  for  they 
spread  their  nets  here  to  catch  the  unwary  but  useful  insects.     I  have  not 
seen  the  net  spread  over  the  opening  in  the  spathe,  but  it  is  spread  over  the 
spadix  within,  reaching  from  tip  to  tip  of  either  the  stigmas,  or  stamens,  or 
both.     Behind  the  spadix  crouches  the  spider-trapper.     The  insect  crawls 
over  the  edge  of  the  spadix,   and  plunges  unsuspectingly  into  the  dimly 
lighted    chamber   below,  where  it  becomes  entangled  in  the  meshes  of  the 
net. 

Flowers  in  which  the  ripening  of  the  anthers  and  maturing  of  the  stigmas 
occur  at  different  times  are  also  said  to  be  dichogamous. 

854  Pollination  of  jack-in-  the-pulpit.  —  The  jacl<-in-the-pulpit  (Arisaema 
triphvUum    has  made  greater  advance  in  the  art  of  enforcing  cross  pollina 
J:iop.   The  larger  number  of  plants  here  are,  as  we  have  found,  dioecious,  the 
staminate  flowers  being  on  the  spadix  of  one  plant,  while  the  pistillate  flowers 
are  on  the  spadix    of   another.      In    a  few  plants,  however,  we  find  both 
female  and  male  flowers  on  the  same  spadix. 

855  The    pretty   bellflower    (Campanula    rotundifolia)    is    dichogamous 
and  proterandrous   (fig.  462).     Many  of  the  composites  are  also  dichoga- 


856. Pollination  of  orchids.—  'But  some  of  the  most  marvellous  adaptations 
for  cross  pollination  by  insects  are  found  in  the  orchids,  or  members  of  the 
orchis  family.  The  larger  number  of  the  members  of  this  family  grow  in  the 
tropics.  Many  of  these  in  the  forests  are  supported  in  lofty  trees  where  they 
are  brought  near  the  sunlight,  and  such  are  called  "epiphytes."  A  Tiumbef 
of  species  of  orchids  are  distributed  in  temperate  regions. 


POLLINA  TION. 


443 


857.  Cypripedium,  or  lady-slipper. — -One  species  of  the  lady-slipper  is 
shown  in  fig.  468.     The  labellum  in  this  genus  is  shaped  like  a  shoe,  as  one 


Fig.  461. 
A  group  of  jacks. 

can  see  by  the  section  of  the  flower  in  fig.  468.  The  stigma  is  situated  at  st, 
while  the  anther  is  situated  at  a,  upon  the  style.  The  insect  enters  about 
the  middle  of  the  boat-shaped  labellum.  In  going  out  it  passes  up  and  out 


444 


RELATION    TO   ENVIRONMENT. 


at  the  end  near  the  flower  stalk.     In  doing  this  it  passes  the  stigma  first  and 
the  anther  last,  rubbing  against  both.      The  pollen  caught  on  the  head  of 


Fig.  462. 

Proterandry  in  the  bell-flower  (campanula).  Lert  figure  shows  the  s-ngencecious  stamens 
surrounding  the  immature  style  and  stigma.  Middle  figure  shows  the  immature  stigma  being 
pushed  through  the  tube  and  brushing  out  the  pollen  ;  while  in  the  right-hand  figure,  after 
the  pollen  has  disappeared,  the  lobes  of  the  stigma  open  out  to  receive  pollen  from  another 
flower. 

the  insect,  will  not  touch  the  stigma  of  the  same  flower,  but  will  be  in  posi- 
tion to  come  in  contact  with  the  stigma  of  the  next  flower  visited 

858.  Epipactis. — In  epipactis  the  action  of  the  pollinia,  which  move 
.downward,  is  described  in  fig.  469. 


Fig.  463- 

Kalmia  latifolia,  showing  position  of  anthers  before  insect  visits,  and  at  the  right  the 
scattering  of  the  pollen  when  disturbed  by  insects.  Middle  figure  section  of  flower. 

849.  In  some  of  the  tropical  orchids  the  pollinia  are  set  free  when  the  insect 
touches  a  certain  part  of  the  flower,  and  are  thrown  in  such  a  way  that  the 
disk  of  the  pollinium  strikes  the  insect's  head  and  stands  upright.  By  the 
time  the  insect  reaches  another  flower  the  pollinium  has  bent  downward  suffi- 


POLLINA  TION, 


445 


ciently  to  strike  against  the  stigma  when  the  insect  alights  on  the  labellum. 
In  the  mountains  of  North  Carolina  I  have  seen  a  beautiful  little  orchid,  in 
which,  if  one  touches  a  certain  part  of  the  flower  with  a  lead-pencil  or  other 
suitable  object,  the  pollinium  is  set  free  suddenly,  turns  a  complete  somer- 
sault in  the  air,  and  lands  with  the  disk  sticking  to  the  pencil.  Many  of  the 


Fig.  464. 
Spray  of  leaves  and  flowers 
of  cytisus. 


orchids  grown  in  conservatories  can  be  used  to  demonstrate  some  of  these 
peculiar  mechanisms. 

860.  Pollination  of  the  canna. — In  the  study  of  some  of  the  marvellous 
adaptations  of  flowers  for  cross  pollination  one  is  led  to  inquire  if,  after  all, 
plants  are  not  intelligent  beings,  instead  of  mere  automatons  which  respond 


Fig.  465- 
Flower  of  cytisus  grown  in  conservatory.     Same  flower  scattering  poller. 


to  various  sorts  of  stimuli.  No  plant  has  puzzled  me  so  much  in  this  respect 
as  the  canna,  and  any  one  will  be  well  repaid  for  a  study  of  recently  opened 
flowers,  even  though  it  may  be  necessary  to  rise  early  in  the  morning  to 
unravel  the  mystery,  before  bees  or  the  wind  have  irritated  the  labellum. 
The  canna  flower  is  a  bewildering  maze  of  petals  and  petal-like  members. 


446 


RELATION    TO   ENVIRONMENT. 


The  calyx  is  green,  adherent  to  the  ovary,  and  the  limb  divides  into  three, 
lanceolate  lobes.  The  petals  are  obovate  and  spreading,  while  the  stamens 
have  all  changed  to  petal-like  members,  called  staminodia.  Only  one  still 
shows  its  stamen  origin,  since  the  anther  is  seen  at  one  side,  while  the  fila- 
ment is  expanded  laterally  and  upwards  to  form  the  staminodium. 


Fig.  466. 

Spartium,  showing  the  dusting  of  the  pollen  through  the  opening  keels  on  the  under  side 
an  insect.     (From  Kerner  and  Oliver.) 


of  an 


861,  The  ovary  has  three  locules,  and  the  three  styles  are  usually  united 
into  a  long,  thin,  strap-shaped  style,  as  seen  in  the  figure,  though  in  some 
cases  three,  nearly  distinct,  filamentous  styles  are  present.  The  end  of  this 
strap-shaped  style  has  a  peculiar  curve  on  one  side,  the  outline  being  some- 


POLLINA  TION. 


447 


times  like  a  long  narrow  letter  S.     It  is  on  the  end  of  this  style,  and  along 
the  crest  of  this  curve,  that  the  stigmatic  surface  lies,  so  that  the  pollen 
/\  A 


Fig.  468. 

Section  of  flower  of  cypripedium.  st, 
stigma  ;  a,  at  the  left  stamen.  The  insect 
enters  the  labellum  at  the  center,  passes 
under  and  against  the  stigma,  and  out 
through  the  opening  b,  where  it  rubs 
against  the  pollen.  In  passing  through 
another  flower  this  pollen  is  rubbed  off 
on  the  stigma. 

must  be  deposited  on  the  stigmatic  end  or  margin 
in  order  that  fertilization  may  take  place. 
Fig.  467.  862.   If  we  open  carefully  canna-flower  buds 

Cypripedium.  which  are  nearly  ready   to   open   naturally,  by 

unwrapping  the  folded  petals  and  staminodia,  we  shall  see  the  anther-bearing 


Fig.  46g. 

Epipactis  with  portion  of  perianth  removed  to  show  details.  /,  labellum ;  s/,  stigma ;  r, 
rostellum ;  /,  pollinium.  When  the  insect  approaches  the  flower  its  head  strikes  the  disk 
of  the  pollinium  and  pulls  the  pollinium  out.  At  this  time  the  pollinium  stands  up  out  of  the 
way  of  the  stigma.  By  the  time  the  insect  moves  to  another  flower  the  pollinia  have  moved 
downward  so  that  they  are  in  position  to  strike  the  stigma  and  leave  the  pollen.  At  the 
right  is  the  head  of  a  bee,  with  two  pollinia  (a)  attached. 


448 


RELATION   TO  ENVIRONMENT. 


staminodium  is  so  wrapped  around  the  flattened  style  that  the  anther  lies 

closely  pressed  against  the  face  of  the  style,  near  the  margin  opposite  that 

on  which  the  stigma  lies. 

863.  The  walls  of  the  anther  locules  which  lie  against  the  style  become 

changed  to  a  sticky  substance  for  their  entire  length,  so  that  they  cling 

firmly  to  the  surface  of  the  style 
and  also  to  the  mass  of  pollen 
within  the  locules.  The  result  is 
that  when  the  flower  opens,  and 
this  staminodium  unwraps  itself 
from  the  embrace  of  the  style,  the 
mass  of  pollen  is  left  there  de- 
posited, while  the  empty  anther  is 
turned  around  to  one  side. 

668.  Why  does  the  flower  de- 
posit its  own  pollen  on  the  style  ? 
Some  have  regarded  this  as  the  act 
of  pollination,  and  have  concluded, 
therefore,  that  cannas  are  neces- 
sarily self  pollinated,  and  that 
cross  pollination  does  not  take 
place.  But  why  is  there  such  evi- 
dent care  to  deposit  the  pollen  on 

,  F[S-  470.  the  side  of  the  style  away  from  the 

Canna   flowers  with  the  perianth  'removed  to       .  .  .     ->      Tr  .   .      , 

show  the  depositing  of  the  po.len  on  the  style  by  stlgmatlC  margin  ?      If  we  visit  the 
the  stamen.  cannas     some     morning,    when    a 

number  of  the  flowers  have  just  opened,  and  the  bumblebees  are  humming 
around  seeking  for  nectar,  we  may  be  able  to  unlock  the  secret. 

864.  We  see  that  in  a  recently  opened  canna  flower,  the  petal  which 
directly  faces  the  style  in  front  stands  upward  quite  close  to  it,  so  that  the 
flower  now  is  somewhat  funnelshaped.     This  front  petal  is  the  labellum,  and 
is  the  landing  place  for  the  bumblebee  as  he  alights  on  the  flower.       Here 
he  comes  humming  along  and  alights  on  the  labellum  with  his  head  so  close 
to  the  style  that  it  touches  it.     But  just  the  instant  that  the  bee  attempts  to 
crowd  down  in  the  flower  the  labellum  suddenly  bends  downward,  as  shown 
in  fig.  468.       In  so  doing  the  head  of  the  bumblebee  scrapes  against  the 
pollen,  bearing  some  of  it  off.     Now  while  the  bee  is  sipping  the  nectar  it  is 
too  far  below  the  stigma  to  deposit  any  pollen  on  the  latter.    When  the  bum- 
blebee flies  to  another  newly  opened  flower,  as  it  alights,  some  of  the  pollen 
of  the  former  flower  is  brushed  on  the  stigma. 

865.  One   can   easily  demonstrate  the   sensitiveness  of  the  labellum  of 
recently  opened  canna  flowers,  if  the  labellum  has  not  already  moved  down 
in  response  to  some  stimulus.     Take  a  lead-pencil,  or  a  knife  blade,  or  even 


POLLINA  TION. 


449 


the  finger,   and  touch  the  upper  surface  of  the  labellum  by  thrusting  it 
between  the  latter  and  the  style.     The  labellum  curves  quickly  downward. 

866.   Sometimes  the  bumblebees,  after  sipping  the  nectar,  will  crawl  up 
over  the  style  in  a  blundering  manner.     In  this  way  the  flower  may  be  pol- 


Fig.  47i. 
Pollination  of  the  canna  flower  by  bumblebee. 


Canna  flower, 
men  at  left. 


Pollen  on  style,  sta- 


linated  with  its  own  pollen,  which  is  equivalent  to  relf  pollination.  Un- 
doubtedly self  pollination  does  take  place  often  in  flowers  which  are  adapted. 
to  a  greater  or  less  degree,  for  cross  pollination  by  insects. 


CHAPTER  XLIV. ' 
THE    FRUIT. 

I.   Parts  of  the  Fruit.- 

867.  After  the  flower  comes  the  fruit. — With  the  perfection  of 
the  fruit  the  seed  is  usually  formed.     This  is  the  end  towards 
which  the  energies  of  the  plant  have  been  directed.     While  the 
seed  consists  only  of  the  ripened  ovule  and  the  contained  em- 
bryo, the  fruit  consists  of  the  ripened  ovary  in  addition,  and  iiv 
many  cases  with  other  accessory  parts,  as  calyx,  receptacle,  etc., 
combined  with  it.     The  wall  of  the  ripened  ovary  is  called  a 
pericarp,  and  the  walls  of  the  ovary  form  the  walls  of  the  fruit. 

868.  Pericarp,  endocarp,  exocarp,  etc. — This  is  the  part  of 
the  fruit  which  envelops  the  seed  and  may  consist  of  the  carpels 
alone,  or  of  the  carpels  and  the  adherent  part  of  the  receptacle, 
or  calyx.     In  many  fruits  the  pericarp  shows  a  differentiation 
into  layers,  or  zones  of  tissue,  as  in  the  cherry,  peach,  plum,  etc. 
The  outer,  which  is  here  soft  and  fleshy,  is  exocarp,  while  the 
inner,  which  is  hard,  is  the  endocarp.     An  intermediate  layer  is 
sometimes  recognized  and  is  called  mesocarp.     In  such  cases 
the  skin  of  the  fruit  is  recognized  as  the  eplcarp.     Epicarp  and 
mesocarp  are  more  often  taken  together  as  exocarp. 

In  general  fruits  are  dry  or  fleshy.  Dry  fruits  may  be 
grouped  under  two  heads.  Those  which  open  at  maturity  and 
scatter  the  seed  are  dehiscent  Those  which  do  not  open  are 
indehiscent. 

450 


THE  FRUIT. 


451 


Fig.  472. 

Seed,  or  akene, 

of  buttercup. 


II.  Indehiscent  Fruits. 

869.  The  akene. — The  thin  dry  wall  of  the  ovary  encloses 
the  singlei  seed.    It  usually  does  not  open  and  free  the  seed 
within.     Such  a  fruit  is  an  akene.     An  akene  is 

a  dry,  indehiscent  fruit.  All  of  the  crowded  but 
separate  pistils  in  the  buttercup  flower  when  ripe 
make  a  head  of  akenes,  which  form  the  fruit  of 
the  buttercup.  Other  examples  of  akenes  are 
found  in  other  members  of  the  buttercup  family, 
also  in  the  composites,  etc.  The  sunflower  seed 
is  a  good  example  of  an  akene. 

870.  The  samara. — The  winged  fruits  of  the  maple  (fig.  574), 
elm,  etc.,   are  indehiscent  fruits.     They  are   sometimes  called 

key  fruits. 

871.  The  caryopsis  is  a  dry 
fruit  in  which  the  seed  is  con- 
solidated with  the  wall  of  the 
ovary,  as  in  the  wheat,  corn, 
and  other  grasses. 

872.  The    schizocarp   is    a 
dry  fruit  consisting  of  several 
locules    (from     a     syncarpous 
gyncecium).    At    maturity    the 

carpels  separate  from  each  other,  but  do  not  themselves  dehisce 
and  free  the  seed,  as  in  the  carrot  family,  mallow  family. 

873.  The  acorn. — The  acorn  fruit  consists  of  the  acorn  and 
the  "cup"  at  the  base  in  which  the  acorn  sits.  The  cup  is  a 
curious  structure,  and  is  supposed  to  be  composed  of  an  involucre 
of  numerous  small  leaves  at  the  base  of  the  pistillate  flower, 
which  become  consolidated  into  a  hard  cup-shaped  body.  When 
the  acorn  is  ripe  if  easily  separates  from  the  cup,  but  the  hard 
pericarp  forming  the  "shell"  of  the  acorn  remains  closed.  Frost 
may  cause  it  to  crack,  but  very  often  the  pericarp  is  split  open  at 
the  smaller  end, by  wedge-like  pressure  exerted  by  the  emerging 
radicle  during  germination. 


Fig.  473- 
Fruit  of  red  oak.     An  acorn'. 


45 2  RELATION   TO  ENVIRONMENT. 

874.  The  hazelnut,  chestnut,  and  beechnut. — In  these  fruits  a 
crown  of  leaves  (involucre)  at  the  base  of  the  flower  grows  around 


Fig.  474- 
Germinating  acorn  of  white  oak. 

the  nut  and  completely  envelops  it,  forming  the  husk  or  burr. 
When  the  fruit  is  ripe  the  nut  is  easily  shelled  out  from  the  husk. 
In  the  beechnut  and  chestnut  the  burr  dehisces  as  it  dries  and 
allows  the  nut  to  drop  out.  But  the  fruit  is  not  dehiscent,  since 
the  pericarp  is  still  intact  and  encloses  the  seed. 

875.  The  hickory-nut,  walnut,  and  butternut. — In  these  fruits 
the  "shuck"  of  the  hickory-nut  and  the  "hull"  of  the  walnut 
and  butternut  are  different  from  the  involucre  of  the  acorn  or 
hazelnut,  etc.     In  the  hickory-nut  the  "shuck"  probably  con- 
sists partly  of  calyx  and  partly  of  involucral  bracts  consolidated, 
probably  the  calyx  part  predominating.     This  part  of  the  fruit 
splits  open  as  it  dries  and  frees  the  "nut,"  the  pericarp  being 
very  hard  and  indehiscent.     In  the  walnut  and  butternut  the 
"hull"  is  probably  of  like  origin  as  the  "shuck"  of  the  hickory 
nut,  but  it  does  not  split  open  as  it  ripens.     It  remains  fleshy. 
The  walnut  and  butternut  are  often  called  drupes  or  stone  fruits, 
but  the  fleshy  part  of  the  fruit  is  not  of  the  same  origin  as  the 
fleshy  part  of  the  true  drupes,  like  the  cherry,  peach,  plum,  etc. 

III.  Dehiscent  Fruits. 

876.  Of  the  dehiscent  fruits  several  prominent  types  are  rec- 
ognized, and  in  general  they  are  sometimes  called  pods.     There 
is  a  single  carpel  (simple  pistil),  and  the  pericarp  is  dry  (gynce- 


THE  FRUIT.  453 

cium  apocarpous) ;  or  where  there  are  several  carpels  united  the 
pistil  is  compound  (gyncecium  syncarpous). 

877.  The  capsule. — When  the  capsule  is  syncarpous  it  may 
dehisce  in   three   different   ways:     ist.  When   the   carpels   split 
along  the  line  of  their  union 

with  each  other  longitudi- 
nally  (septicidal  dehiscence), 
as  in  the  azalea  or  rhodo- 
dendron.  2d.  When  the  Fig.  475. 

i         1.7 'f    J  ii  •  J         Diagrams  illustrating  three  types  (in  cross- 

Carpels  Split  down  the  mid-  section)  of  the  dehiscence  of  dry  Wits.  Loc, 
die  line  (loculiddal  dehlS-  loculicida1'  Se*>  Septicidal.  Septifragal. 

cence),  as  in  the  fruit  of  the  iris,  lily,  etc.  3d.  When  the  carpels 
open  by  pores  (poricidal  dehiscence),  as  in  the  poppy.  Some 
syncarpous  capsules  have  but  one  locule,  the  partitions  between 
the  different  locules  when  young  having  disappeared.  The 
"bouncing-bet"  is  an  example,  and  the  seeds  are  attached  to  a 
central  column  in  four  rows  corresponding  to  the  four  locules 
present  in  the  young  stage. 

878.  A  follicle  is  a  capsule  with  a  single  carpel  which  splits 
open  along  the  ventral  or  upper  suture,  as  in  the  larkspur,  peony. 

879.  The  legume,  or  true  pod,  is  a  capsule  with  a  single  carpel 
which  splits  along  both  sutures,  as  the  pea,  bean,  etc.     As  the  pod 

ripens  and  dries,  a  strong  twisting  ten- 
sion is  often  produced,  which  splits  the 
pod  suddenly,  scattering  the  seeds. 

880.  The  silique.— In    the  toothwort, 
shepherd' s-purse,  and  nearly  all  of  the 
plants  in  the  mustard  family  the    fruit 
consists    of    two    united    carpels,    which 
separate  at    maturity,  leaving    the    par- 
tition wall  persistent.        Such  a  fruit  is 
a  silique;  when  short  it  is  a  silicic,  or 
pouch. 

881.  A  pyxidium,  or  pyxis,  is  a  cap- 
sule which  opens  with  a  lid,  as  in  the 

Fruitof^e^a-.apod. 


454 


RELATION   TO  ENVIRONMENT. 


IV.  Fleshy  and  Juicy  Fruits. 

882.  The  drupe,  or  stone-fruit.— In  the  plum,  cherry,  peach, 
apricot,  etc.,  the  outer  portion  (exocarp)  of  the  pericarp  (ovary) 
becomes  fleshy,  while  the  inner  portion  (endocarp)  becomes  hard 
and  stony,  and  encloses  the  seed,  or  "pit."    Such  a  fruit  is  known 
as  a  drupe,  or  as  a  stone-fruit.     In  the  almond  the  fleshy  part 
of  the  fruit  is  removed. 

883.  The  raspberry  and  blackberry.— While  these  fruits  are 


Fig.  477. 
Drupe,  or  stone-fruit,  of  plum. 

known  popularly  as  "berries,"  they  are  not  berries  in  the  tech- 
nical sense.  Each  ovary,  or  pericarp,  in  the  flower  forms  a  single 
small  fruit,  the  outer  portion  being  fleshy  and  the  inner  stony,  just 
as  in  the  cherry  or  plum.  It  is  a  drupelet  (little  drupe).  All  of 
the  drupelets  together  make  the  "berry,"  and  as  they  ripen  the 
separate  drupelets  cohere  more  or  less.  It  is  a  collection,  or 
aggregation,  of  fruits,  and  consequently  they  are  sometimes  called 
collective  fruits,  or  aggregate  fruits.  In  the  raspberry  the  fruit 
separates  from  the  receptacle,  leaving  the  latter  on  the  stem, 
while  the  drupelets  of  the  blackberry  and  dewberry  adhere  to 
the  receptacle  and  the  latter  separates  from  the  stem. 


THE  FRUIT. 


455 


884.  The  berry. — In  the  true  berry  both  exocarp  (including 
mesocarp)  and  endocarp  are  fleshy  or  juicy.  Good  examples 
are  found  in  cranberries,  huckleberries,  gooseberries,  currants, 
snowberries,  tomatoes,  etc.  The  calyx  and  wall  of  the  pistil 
are  adnate,  and  in  fruit  become  fleshy  so  that  the  seeds  are  im- 
bedded in  the  pulpy  juice.  The  seeds  themselves  are  more  or 
less  stony.  In  the  case  of  berries,  as  well  as  in  strawberries,  rasp- 
berries, and  blackberries,  the  fruits  are  eagerly  sought  by  birds 
and  other  animals  for  food.  The  seeds  being  hard  are  not 
digested,  but  are  passed  with  the  other  animal  excrement  and 
thus  gain  dispersal. 


V.   Reinforced,  or  Accessory,  Fruits. 

When  the  torus  (receptacle)  is  grown  to  the  pericarp  in  fruit, 
the  fruit  is  said  to  be  reinforced.  The  torus  may  enclose  the 
pericarps,  or  the  latter  may  be  seated  upon  the  torus. 

885.  In  the  strawberry  the  receptacle  of  the  flower  becomes 


Fig.  478. 
Fruit  of  raspberry. 


larger  and  fleshy,  while  the  "seeds,"  which  are  akenes,  are  sunk 
in  the  surface  and  are  hard  and  stony.     The  strawberry  thus 


RELATION  TO  ENVIRONMENT. 

differs  from  the  raspberry  and  blackberry,  but  like  them  it  is 
not  a  true  berry. 

886.  The  apple,  pear,  quince,  etc.— In  the  flower  the  calyx, 
corolla,  and  stamens  are  perigynous,  i.e.,  they  are  seated  on  the 
margin  of  the  receptacle,  or  torus,  which  is  elevated  around  the 
pistils.     In  fruit  the  receptacle  becomes  consolidated  with  the 
wall  of  the  ovary   (with  the  pericarp).     The  torus  thus  rein- 
forces the  pericarp.     The  torus  and  outer  portion  of  the  pericarp 
become  fleshy,  while  the  inner  portion  of  the  pericarp  becomes 
papery  and  forms  the  "core."     The  calyx  persists  on  the  free 
end  of  the  fruit.     Such  a  fruit  is  called  a  pome.     The  receptacle, 
or  torus,  of  the  rose-flower,  closely  related  to  the  apple,  is  in- 
structive when  used  in  comparison.     The   rose-fruit  is  called  a 
"hip." 

887.  The  pepo. — The  fruit  of  the  squash,  pumpkin,  cucum- 
ber, etc.,  is  called  a  pepo.     The  outer  part  of  the  fruit  is  the  recep- 
tacle (or  torus),  which  is  consolidated  with  the  outer  part  of  the 
three-loculed  ovary.     The  calyx,  which,   with  the  corolla  and 
stamens,  was  epigynous,  falls  off  from  the  young  fruit. 

VI.  Fruits  of  Gymnosperms. 

The  fruits  of  the  gymnosperms  differ  from  nearly  all  of  the 
angiosperms  in  that  the  seed  formed  from  the  ripened  ovule  is 
naked  from  the  first,  i.e.,  the  ovary,  or  carpel,  does  not  enclose 
the  seed. 

888.  The  cone-fruit  is  the  most  prominent  fruit  of  the  gymno- 
sperms, as  can  be  seen  in  the  cones  of  various  species  of  pine, 
spruce,  balsam,  etc. 

889.  Fleshy  fruits  of  the  gymnosperms. — Some  of  the  fleshy 
fruits  resemble  the  stone-fruits  and  berries  of  the  angiosperms. 
The  cedar  "berries,"  for  example,  are  fleshy  and  contain  several 
seeds.     But  the  fleshy  part  of  the  fruit  is  formed,  not  from  peri- 
carp, since  there  is  no  pericarp,  but  from  the  outer  portion  of 
the  ovules,  while  the  inner  walls  of  the  ovules  form  the  hard 
stone  surrounding  the  endosperm  and  embryo.     An  examination 


THE  FRUIT.  457 

of  the  pistillate  flower  of  the  cedar  (juniper)  shows  usually  three 
flask-shaped  ovules  on  the  end  of  a  fertile  shoot  subtended  by  as 
many  bracts  (carpels?).  The  young  ovules  are  free,  but  as  they 
grow  they  coalesce,  and  the  outer  walls  become  fleshy,  forming 
a  berry-like  fruit  with  a  three-rayed  crevice  at  the  apex  marking 
the  number  of  ovules.  The  red  fleshy  fruit  of  the  yew  (taxus) 
resembles  a  drupe  which  is  open  at  the  apex.  The  stony  seed 
is  formed  from  the  single  ovule  on  the  fertile  shoot,  while  the  red 
cup-shaped  fleshy  part  is  formed  from  the  outer  integument  of 
the  ovule.  The  so-called  "aril"  of  the  young  ovule  is  a  rudi- 
mentary outer  integument. 

The  fruit  of  the  maidenhair  tree  (ginkgo)  is  about  the  size  of 
a  plum  and  resembles  very  closely  a  stone-fruit.  But  it  is  merely 
a  ripened  ovule,  the  outer  layer  becoming  fleshy  while  the  inner 
layer  becomes  stony  and  forms  the  pit  which  encloses  the  em- 
bryo and  endosperm.  The  so-called  "aril,"  or  "collar,"  at  the 
base  of  the  fruit  is  the  rudimentary  carpel,  which  sometimes  is 
more  or  less  completely  expanded  into  a  true  leaf.  The  fruit 
of  cycas  is  similar  to  that  of  ginkgo,  but  there  is  no  collar  at  the 
base.  In  zamia  the  fruit  is  more  like  a  cone,  the  seeds  being 
formed,  however,  on  the  under  sides  of  the  scales. 

VII.  The  "Fruit"  of  Ferns,  Mosses,  etc. 

890.  The  term  "fruit"  is  often  applied  in  a  general  or  popu- 
lar sense  to  the  groups  of  spore-producing  bodies  of  ferns  (fruit- 
dots,  or  sori),  the  spore-capsules  of  mosses  and  liverworts,  and 
also  to  the  fruit-bodies,  or  spore-bearing  parts,  of  the  fungi  and 
algae. 


CHAPTER  XLV. 


SEED   DISPERSAL. 

891.  Means  for  dissemination  of  seeds. — During  late  summer  or  autumn 
a  walk  in  the  woods  or  afield  often  convinces  us  of  the  perfection  and  variety 
of  means  with  which  plants  are  provided  for  the  dissemination  of  their 
seeds,  especially  when  we  discover  that  several  hundred  seeds  or  fruits  of 
different  plants  are  stealing  a  ride  at  our  expense  and  annoyance.  The  hooks 
and  barbs  on  various  seed -pods  catch  into  the  hairs  of  passing  animals  and 
the  seeds  may  thus  be  transported 
considerable  distances.  Among  the 
plants  familiar  to  us,  which  have  such 
contrivances  for  unlawfully  gaining 
transportation,  are  the  beggar-ticks 
or  stick  tights,  or  sometimes  called 


Fig.  479. 

Bur  of  bidens  or  bur-marigold,  show- 
ing barbed  seeds. 


-  Fig.  480. 

Seed  pod  of  tick-treefoil  (desmodium) ;  at  the 
right  some  of  the  hooks  greatly  magnified. 


bur-marigold  (bidens),  the  tick-treefoil  (desmodium),  or  cockle-bur  (xanthi- 
um),  and  burdock  (arctium). 

892.  Other  plants  like  some  of  the  sedges,  etc.,  living  on  the  margins  of 
streams  and  of  lakes,  have  seeds  which  are  provided  with  floats.  The  wind 
or  the  flowing  of  the  water  transports  them  often  to  distant  points. 

458 


SEED  DISPERSAL. 


459 


893.  Many  plants  pos  ess  attractive  devices,  and  offer  a  substantial 
reward,  as  a  price  for  the  distribution  of  their  seeds.  Fruits  and  berries  are 
devoured  by  birds  and  other  animals  ;  the  seeds  within,  often  passing  un- 
harmed, may  be  carried  long  distances.  Starchy  and  albuminous  seeds  and 


Fig.  481. 
Seeds  of  geum  showing  the  booklets  where  the  end  of  the  style  is  kneed. 

grains  are  also  devoured,  and  while  many  such  seeds  are  destroyed,  others 
are  not  injured,  and  finally  are  lodged  in  suitable  places  for  growth,  often 
remote  from  the  original  locality.  Thus  animals  willingly  or  unwillingly 
become  agents  in  the  dissemination  of  plants  over  the  earth.  Man  in  the 
development  of  commerce  is  often  responsible  for  the  wide  distribution  of 
harmful  as  well  as  beneficial  species. 

894.  Other  plants  are  more  independent,  and  mechanisms  are  employed 
for  violently  ejecting  seeds  from  the  pod  or  fruit.  The  unequal  tension  of 
the  pods  of  the  common  vetch  (Vicia  sativa)  when  drying  causes  the  valves 
to  contract  unequally,  and  on  a  dry  summer  day  the  valves  twist  and  pull  in 
opposite  directions  until  they  suddenly  snap  apart,  and  the  seeds  are  thrown 
forcibly  for  some  distance.  In  the  impatiens,  or  touch-me-not  as  it  is  better 
known,  when  the  pods  are  ripe,  often  the  least  touch,  or  a  pinch,  or  jar,  sets 
the  five  valves  free,  they  coil  up  suddenly,  and  the  small  seeds  are  thrown 
for  several  yards  in  all  directions.  During  autumn,  on  dry  days,  the  pods 
of  the  witch  hazel  contract  unequally,  and  the  valves  are  suddenly  spread 
apart,  and  the  seeds  are  hurled  away. 

Other  plants  have  seeds  provided  with  tufts  of  pappus,  or  hair-like 
masses,  or  wing-like  outgrowth.*  which  serve  to  buoy  them  up  as  they 


460 


RE  LA  TION  TO  ENVIRONMENT. 


are  whirled  along,  often  miles  away.  In  late  spring  or  early  summer 
the  pods  of  the  willow  burst  open,  exposing  the  seeds,  each  with  a  tuft 
of  white  hairs  making  a  mass  of  soft  down.  As  the  delicate  hairs  dry, 


Fig.  482. 

Touch-me-not  (Impatiens  fulva);  side  and  front  view  of  flower  below;  above  unopened 
pod,  and  opening  to  scatter  the  seed. 

they  straighten  out  in  a  loose  spreading  tuft,  which  frees  the  individual  seeds 
from  the  compact  mass.  Here  they  are  caught  by  currents  of  air  and  float 
off  singly  or  in  small  clouds. 

895.  The  prickly  lettuce. — In  late  summer  or  early  autumn  the  seeds  of 
the  prickly  lettuce  (Lactuca  scariola)  are  caught  up  from  the  roadsides  by 
the  winds,  and  carried  to  fields  where  they  are  unbidden  as  well  as  unwel- 
come guests.     This  plant  is  shown  in  fig.  483. 

896.  The  wild  lettuce. — A  related  species,  the  wild  lettuce  (Lactuca  cana- 
densis)  occurs  on  roadsides  and  in  the  borders  of  fields,  and  is  about  one 
meter  in  height.     The  heads  of  small  yellow  or  purple  flowers  are  arranged 
in  a  loose  or  branching  panicle.     The  flowers  are  rather  inconspicuous,  the 
rays  projecting  but  little  above  the  apex  of  the  enveloping  involucral  bracts, 
which  closely  press  together,  forming  a  flower-head   more   or   less    flask- 
shaped. 

At  the  time  of  flowering  the  involucral  bracts  spread  somewhat  at  the 
apex,  and  the  tips  of  the  flowers  are  a  little  more  prominent.  As  the  flowers 
then  wither,  the  bracts  press  closely  together  again  and  the  head  is  closed. 
As  the  seeds  ripen  the  bracts  die,  and  in  drying  bend  outward  and  down- 
ward, around  the  flower  stem  below,  or  they  fall  away.  The  seeds  are 


SEED    DISPERSAL. 


461 


thus  exposed.  The  dark  brown  achenes  stand  over  the  surface  of  the  recep- 
tacle, each  one  tipped  with  the  long  slender  beak  of  the  ovary.  The  "  pap- 
pus," which  is  so  abundant  in  many  of  the  plants  belonging  to  the  composite 
family,  forms  here  a 
pencil-like  tuft  at  the 
tip  of  this  long  beak. 
As  the  involucral  bracts 
dry  and  curve  down- 
ward, the  pappus  also 
dries,  and  in  doing  so 
bends  downward  and 
stands  outward,  brist- 
ling like  the  spokes  of 
a  small  wheel.  It  is  an 
interesting  coincidence 
that  this  takes  place 
simultaneously  with 
the  pappus  of  all  the 
seeds  of  a  head,  so 
that  the  ends  of  the 
pappus  bristles  of  ad- 
joining seeds  meet, 
forming  a  many-sided 
dome  of  a  delicate  and 
beautiful  texture.  This 
causes  the  beaks  of  the 
achenes  to  be  crowded 
apart,  and  with  the 
leverage  thusbroughtto 
bear  upon  the  achenes 
they  are  pried  off  the 
receptacle.  They  are 
thus  in  a  position  to 
be  wafted  away  by  the 
gentlest  zephyr,  and 
they  go  sailing  away 
on  the  wind  like  a 
miniature  parachute. 
As  they  come  slowly 


Fig.  483- 
Lactuca  scariola. 


to  the  ground  the  seed 
is  thus   carefully  low- 
ered first,   so  that  it  touches  the  ground  in  a  position  for  the  end  which 
contains  the  root  of  the  embryo  to  come  in  contact  with  the  soil. 


462 


RELATION   TO   ENVIRONMENT. 


897.  The  milkweed,  or  silkweed.— The  common  milkweed,  or  silkweed 
(Asclepias  cornuti),  so  abundant  in  rich  grounds,   is   attractive  not   only 


Fig.  484. 
Milkweed  (Asclepias  cornuti);  dissemination  of  seed. 

because  of  the  peculiar  pendent  flower  clusters,  but  also  for  the  beautiful 
floats  with  which  it  sends  its  seeds  skyward,  during  a  puff  of  wind,  to  finally 
lodge  on  the  earth. 

898.  The  large  boat-shaped,  tapering  pods,  in  late  autumn,  are  packed 
with  oval,  flattened,  brownish  seeds,  which  overlap  each  other  in  rows  like 
shingles  on  a  roof.     These  make  a  pretty  picture  as  the  pod  in  drying  splits 
along  the  suture  on  the  convex  side,  and  exposes  them  to  view.     The  silky 
tufts  of  numerous  long,  delicate  white  hairs  on  the  inner  end  of  each  seed, 
in  drying,  bristle  out,  and  thus  lift  the  seeds  out  of  their  enclosure,  where 
they  are  caught  by  the  breeze  and  borne  away  often  to  a  great  distance, 
where  they  will  germinate  if  conditions  become  favorable,  and  take  their 
places  as  contestants  in  the  battle  for  existence. 

899.  The  virgin's  bower. — The  virgin's  bower  (Clematis  virginiana),  too, 
clambering  over  fence  and  shrub,  makes  a  show  of  having  transformed  its 


SEED   DISPERSAL. 


463 


exquisite  white  flower  clusters  into  grayish -white  tufts,  which  scatter  in  the 
autumn  gusts  into  hundreds  of  arrow-headed,  spiral  plumes.     The  achenes 


Fig.  485- 
Seed  distribution  of  virgin's  bower  vclematis). 

have  plumose  styles,  and  the  spiral  form  of  the  plume  gives  a  curious  twist 
to  the  falling  seed  (fig.  485). 


PART  IV. 

VEGETATION    IN   RELATION   TO  ENVIRONMENT. 

CHAPTER  XLVI. 

FACTORS    INFLUENCING    VEGETATION    TYPES; 
OR    ECOLOGICAL    FACTORS. 

900.  In  studying  the  life  and  growth  of  plants  it  becomes  very 
apparent  that  from  the  germination  of  the  seed  to  the  production 
of  flowers  and  fruit  the  plant  is  dependent  upon  the  favorable 
influence  of  certain  conditions  of  environment.  A  dry  seed  kept 
in  dry  air  or  dry  soil  will  never  germinate,  or  if  it  is  kept  in  moist 
soil,  the  temperature  of  which  is  below  a  certain  minimum  (from 
6°  C.  to  o°  C.),  it  will  remain  apparently  lifeless.  But  with  a 
favorable  amount  of  moisture  and  heat  the  life  which  was  dor- 
mant becomes  active,  growth  begins,  the  embryo  is  nourished 
by  stored  food,  the  root  lays  hold  of  the  soil  for  support,  and  the 
stem  and  leaves  rise  to  the  light.  Light  now  exercises  an  influ- 
ence on  the  form  and  position  of  the  leaves  as  well  as  on  color 
and  work.  The  root  takes  up  watery  food  substances  from  the 
soil.  If  the  soil  contains  too  much  water  or  too  little,  the  plant 
suffers  correspondingly;  or  if  certain  chemical  substances  are 
too  abundant  in  the  soil,  or  if  others  are  lacking,  the  plant  suffers. 
Still  we  know  that  some  plants  do  better  than  others  in  wet  soil 
or  even  in  water  of  lakes  or  ponds,  while  still  other  plants  thrive 
better  in  a  comparatively  dry  soil.  Some  thrive  better  in  rocky 
situations,  some  in  sandy  soil,  some  in  mud,  and  others  in  humus. 

464 


FACTORS  OF  ENVIRONMENT.  46  5 

Some  thrive  exposed  to  strong  sunlight,  others  in  the  shade,  and 
so  on.  Not  only  is  the  individual  plant  influenced  by  these  con- 
ditions of  environment,  but  colonies  or  societies  of  plants,  as 
they  exist  in  a  natural  state,  which  we  call  their  home,  are 
likewise  influenced.  In  fact  these  conditions  of  environment 
largely  determine  the  household  relations  of  plants,  i.e.,  the  eco- 
logical relations,  the  study  of  which  we  call  ecology,  a  study  of 
plants  in  their  home,  or  natural  environment.  These  condi- 
tions are  known  as  ecological  factors.  The  ecological  factors 
are  in  general  of  three  sorts:  ist,  physical  factors;  2d,  climatic 
factors;  3d,  biotic  factors.  Some  of  the  physical  factors  are 
water,  heat,  light,  wind,  chemical  condition  of  the  soil,  physical 
or  mechanical  condition  of  the  soil,  etc.  The  climatic  factors 
are  rainfall  and  general  atmospheric  humidity,  the  broader 
temperature  limits,  great  changes  in  temperature  for  long 
periods.  The  biotic  factors  are  certain  animals,  the  plants 
themselves,  and  even  man. 


I.  Physical  Factors. 

901.  Water.     Importance  of  water. — Water  is   regarded    as 
one  of  the  most  important  of  the  ecological  factors,  though  it 
should  be  borne  in  mind  that  no  factor  is  operative  unless  cer- 
tain other  factors  are  also  favorable.     The  plant  responds  only 
to  the  favorable  action  of  several  of  the  factors,  and  it  is  exceed- 
ingly difficult  to  ascribe  a  definite  value  to  any  one  of  them. 
We  can  study  the  influence  of  one  by  maintaining  a  certain 
degree  of  constancy  of  all  the  others.     That  water  is  a  very  im- 
portant factor,  however,  can  be  seen  from  the  fact  that  most 
plants  contain  a  large  percentage  of  water,  which  in  the  case  of 
land  plants  is  rapidly  lost  by  transpiration,  and  must  be  replaced 
by  absorption  of  more  water  from  the  soil,  while  in  the  case  of 
water  plants  the  effect  of  removing  them  for  even  a  short  while 
from  the,  water  and  exposing  them  to  dry  air  is  easily  seen. 

902.  A  modicum  of  soil- water. — For  all  species  there  is  a 


t 

466  RELATION   TO  ENVIRONMENT. 

physiological  optimum  as  regards  the  necessary  amount  of  water 
in  the  soil,  or  in  all  the  environment,  including  moisture  in  the 
air.  For  many  plants  with  which  we  are  familiar  the  physio- 
logical optimum  of  water  in  the  soil  is  when  the  soil  is  percep- 
tibly moist,  not  dry  to  the  feel,  nor  so  wet  as  to  be  saturated,  of 
so  that  water  can  be  squeezed  from  it  by  pressure  in  the  hand. 
These  plants,  which  usually  have  thin  leaves  for  rapid  trans- 
piration, if  the  water  increases  to  the  point  of  saturation  in  the 
soil,  become  sickly  or  die,  because  there  is  not  sufficient  air  in 
the  soil  to  enable  the  roots  to  absorb  enough  water.  On  the 
other  hand,  if  the  moisture  in  the  soil  diminishes,  as  during  a 
dry  period,  the  plant  often  wilts  and  even  dies. 

903.  Very  dry  soil. — In  regions  where  the  soil  is  very  dry  for 
most  of  the  year,  the  plants  accustomed  to  an  abundance  of 
moisture  will  not  grow.     But  here  we  find  plants  growing  which 
through  long  time  became  accustomed  to  the  conditions  by  being 
modified,  i.e.,  the  root  system  is  enlarged,  so  there  is  more  sur 
face  for  absorption,  while  the  leaf  and  stem  system  is  reduced, 
so  the  leaves  are  small  and  thick,  thus  reducing  the  surface  for 
transpiration,  while  at  the  same  time  providing  a  water  storage 
in  the  thick  leaves,  succulent  leaves,  or  tuberous  roots. 

904.  Excess  of  soil-water. — Now  if  we  turn  to  the  situations 
where  the  soil  is  constantly  saturated  with  water,  or  the  ground 
is  covered  with  shallow  water,  where  plants  accustomed  to  moist 
soil  could  not  grow,  we  likewise  find  plants  growing  which  have 
become  modified  so  as  to  fit  them  to  succeed  under  these  condi- 
tions.    The  system  of  roots  and  root-hairs  is  reduced  because  of 
the  water  and  unfavorable  conditions  for  absorption,  and  cor- 
respondingly we  find  the  leaf  system  usually  reduced   so  that 
transpiration   is   lessened.     In    this    way   water   in    medium   or 
scarce  amounts,  or  in  excess,  exercises  an  influence  on  the  plants. 
But  the  character  of  the  plants  cannot  be  determined  alone  by 
the  amount  of  water  in  the  soil.     The  humidity  of  the  air,  the 
drying  effect  of  wind,  the  effect  of  heat  and  light,  as  well  as  the 
chemical  and  physical  properties  of  the  soil,  are  to  be  taken  into 
account 


FACTORS  OF  ENVIRONMENT. 

905.  Hydrodynamic  forces. — There  should  be  added  also  the 
hydrodynamic  forces  as  a  factor  in  influencing  vegetation.     The 
beating  of  the  waves  on  rocks,  or  the  force  of  the  water  at  water- 
falls, or  in  rapids,  or  flowing  water,  encourages  a  characteristic 
water  flora,  and  water  also  assists  in  the  distribution  of  seeds  or 
plant  parts.     Of  the  greatest  importance  is  the  action  of  water 
in  eroding  the  surface  of  the  earth,  resulting  in  the  so-called  lev- 
elling process;    also  the  effect  of  floods  and  the  cutting  of  the 
channels  for  streams.     The  mechanical  effect  of  precipitation  is 
sometimes  injurious,  especially  in  the  case  of  hail,  and  in  heavy 
snows  which  cling  to  branches  and  weight  them  down. 

906.  Light. — Light  as  an  ecological  factor  influences  plants 
in  several  ways:   ist.  Influence  of  light  in  photosynthesis  enables 
the  plant  to  obtain  the  necessary  carbohydrates.     2d.  The  influ- 
ence of  light  in  the  direction  of  growth  of  stems  and  in  the 
position  assumed  by  leaves  brings  the  plant  organs  in  a  position 
favorable    for    photosynthesis.     3d.  In    very    many    plants    the 
leaves   remain   rudimentary   unless   they   are   in   the   light,    and 
light  in  most  cases  is  necessary  for  the  formation  of  the  green 
chlorophyll.     Since  some  plants  are  able  to  outgrow  other  plants 
Jn  their  adjustment  to  the  light  relation,  many  of  these,  instead 
of  dying  out  for  want  of  brilliant  illumination,  have  accommo- 
dated themselves  to  various  degrees  of  intensity  of  diffused  light, 
as  in  the  case  of  shade  plants    and  deep-water  plants.     Many 
shade  plants  are  injured  when  subjected  to  direct  sunlight,  so 
that  light  as  well  as  water  is  harmful  to  certain  plants  under  cer- 
tain conditions,  and  its  modifying  influence  is  therefore  greater 
in  plant  forms  than  it  otherwise  would  be.     An  abundance  of 
light  is  usually  necessary  for  development  of  flowers  and  fruit. 
Light  also  accelerates  transpiration,  and  is  thus  of  direct  benefit 
to  the  plant  when  supplied  with  an  optimum  of  soil  moisture, 
and  injuries  sometimes  result  to  plants  when  root  absorption  is 
active  and  transpiration  is  slow.     Leaves  exposed  to  direct  sun- 
light have  a  thicker  epidermis  than  shade  leaves,  and  in  the 
latter  the  palisade  layer  of  cells  is  less  developed  and  the  leaves 
are  thinner  and  softer. 


468  RELATION   TO   ENVIRONMENT. 

907.  Heat. — Heat  has  a  great  influence  on  plant  growth  and 
distribution,  as  well  as  upon  the  general  form  of  much  of  the 
earth's  vegetation. 

908.  Vegetation  at  low  temperatures. — Many  arctic  and  al- 
pine plants  are  able  to  vegetate  and  even  fruit  at  extremely  low 
temperatures,  some  of  them  very  near  to  zero  centigrade.     Some 
arctic  algae  fruit  in  the  dark  at  1.8°  C.,  while  many  arctic  plants 
can  exist  at  —  50°  to  —  70°  C.     Spores  of  some  fungi,  bacteria,  and 
algae,  and  certain  dry  seeds,  can  endure  much  lower  tempera- 
tures.    The  growth  period  for  most  vegetation  begins  at  about 
6°  C.  (  =  43°F.),  or  in  the  tropics  at  io°-i2°  C.,  while  often  a 
much  higher  temperature  is  necessary  for  reproduction  of  many 
plants.     Among   the   flowering   plants   annuals   are   largely   ex- 
cluded from  polar  lands,  because  the  summer  season  is  so  short 
that  the  total  available  heat  is  not  sufficient  for  growth  and  repro- 
duction.    Annuals  need  a  longer  time  for  this  than  perennials. 
The  upper  limit  of  temperature  favorable  for  plants  in  general 
is  45°-5o°  C.,  while  the  optimum  is  below  this. 

909.  Very  high  temperatures,  however,  are  injurious  if  not 
fatal  to  most  plants,  though  certain  algae  are  known  to  vegetate 
at  8o°-9o°  C.     Some  desert  plants  are  able  to  resist  a  tempera- 
ture of  70°  C.,  while  some  flowering  plants  are  killed  at  45°. 
Where  plants  or  their  seeds  or  spores  contain  a  large  percentage 
of  water,  they  are  more  easily  killed  by  high  degrees  of  heat  or 
low  degrees  of  cold.     But  dry  seeds  and  spores  are  often  very 
resistant.      Some    air-dry    seeds    will    resist    a    temperature    of 
i2o°-i3o°C.     Spores  of  certain  bacteria  will  resist  a  tempera- 
ture of  130°  C.  for  a  short  time,  while  at  a  temperature  of  iooc- 
110°  they  may  live  for  several  hours.     But  if  allowed  to  germi- 
nate and  thus  pass  into  the  vegetative  condition  in  which  they 
contain  much  more  water,  and  the  protoplasm  is  in  a  less  resist- 
ant condition,  they  are  killed  at  100°  in  a  short  time,  or  even  at 
80°  continued  longer. 

910.  Cardinal  temperature  points  for  different  plant  func- 
tions.— It  has  been  found  in  the  case  of  many  plants  that  for 
the  different  life  functions,  or  separate  processes  in  growth  and 


FACTORS   OF  ENVIRONMENT.  469 

reproduction,  the  temperature  which  is  most  favorable  varies  in 
the  different  processes.  For  each  process  there  is  a  minimum, 
optimum,  and  maximum  temperature,  the  minimum  and  maxi- 
mum representing  the  lowest  and  highest  temperatures  at  which 
the  process  can  take  place,  while  the  optimum  is  the  temperature 
most  favorable  for  the  process.  The  absolute  optimum,  which 
corresponds  to  the  highest  intensity  of  a  function,  therefore  is 
not  always  the  most  favorable  temperature  for  the  plant  as  a 
whole.  For  in  the  case  of  transpiration  and  respiration  at  the 
absolute  optimum  temperature  these  processes  would  take  place 
so  rapidly  that  the  plant  would  be  injured.  On  the  other  hand, 
the  harmonic  optimum  corresponds  to  the  most  favorable  inten- 
sity of  a  function.  So  the  "ecological  optimum  is  composed  of 
the  harmonic  optima."  The  cardinal  temperature  points  are 
the  most  favorable  temperatures  for  the  various  processes. 
From  germination  of  the  seed  through  growth  and  reproduction 
there  is  a  general  rise  of  the  curve  which  represents  the  cardinal 
points  for  the  various  processes,  but  there  is  a  more  or  less  regu- 
lar fluctuation  or  alternation  of  the  successive  cardinal  points; 
especially  is  this  the  case  with  many  plants  in  temperate  and 
arctic  regions.  For  example,  the  cardinal  point  for  the  growth 
function  is  often  higher  than  the  cardinal  point  for  flower  forma- 
tion and  reproduction. 

911.  Acclimatization. — When  plants  are  changed  from  warm 
zones  to  colder  ones,  or  from  cold  zones  to  warmer  ones,  either 
by  man  or  by  the  laws  of  migration,  if  they  are  able  to  reproduce 
and  propagate  themselves  in  the  new  region  it  is  because  they 
have  become  adapted  to  the  changed  conditions  of  temperature. 
This  adaptation  of  an  organism  to  changed  climatic  conditions 
is  called  acclimatization.  Acclimatization  to  changed  temperature 
conditions  is  possible  in  the  case  of  those  plants  which  are  able 
to  adjust  the  cardinal  points  for  the  different  life  processes  to 
the  new  temperatures.  This  is  accomplished  by  raising  or 
lowering  the  cardinal  points  for  the  different  functions.  It  is  a 
well-known  fact  that  some  plants  taken  from  cool  zones  to  warmer 
ones  are  able  to  raise  the  cardinal  points  for  processes  of  nutri- 


47°  RELATION   TO   ENVIRONMENT. 

tion,  assimilation,  and  growth,  so  that  growth  is  much  more  lux- 
uriant than  in  the  cooler  climate,  but  they  fail  to  flower  or  seed 
because  they  are  not  able  to  raise  the  cardinal  point  for  these 
processes.  Such  plants  become  acclimatized  with  reference  to 
certain  functions  only.  So  some  plants  taken  from  warm  cli- 
mates to  cooler  ones  may  grow  well,  but  fail  to  flower  or  fruit 
because  they  cannot  lower  the  cardinal  temperature-point  for 
these  functions  to  meet  the  new  conditions.  Different  species 
vary  in  this  respect.  The  same  species  also  may  possess  the 
power  of  raising  or  lowering  the  cardinal  points  of  all  its  func- 
tions to  a  remarkable  degree,  and  this  probably  accounts  for  the 
very  wide  north-and-south  distribution  of  certain  species. 

912.  Protection  against   cold. — Intense   cold  prevents  root 
absorption,  and  has  a  drying  effect  on  vegetation,  so  that  vege- 
tation protects  itself  in  several  ways  through  the  severe  winter 
in    temperate    and    arctic    climates.      The    deciduous   habit    of 
trees  and  shrubs,  the  underground  stem  of  perennial  herbs,  the 
rosette  habit  of  perennials,  the  bud-scales  on  winter  shoots,  and 
the  low  stature  of  arctic  and  alpine  plants  are  modifications  in 
response  to  the  harmful  effects  of  extreme  cold. 

913.  Effects    of  freezing. — In    freezing   weather   plants    are 
injured  in  three  ways:    ist.  The  chilling  effect  of  cold  is  suffi- 
cient to  kill  some  plants  which  are  very  sensitive  to  low  tem- 
peratures.    2d.  Others   are  killed   even   by   comparatively  light 
frosts,  or  freezes  (examples :  potatoes,  tomatoes,  corn,  many  herbs, 
you  g  leaves  and  shoots  of  many  plants).    In  these  cases  t.ie  injury 
is  chiefly  caused  by  the  loss  cf  water  from  the  protoplasm  in  the 
cells.     As  freezing  takes  place  in  the  tissues  the  ice  crystals  are 
usually  not  formed  within  the  cells.     But  some  of  the  water, 
under  the  influence  of  the  extreme  cold,  is  gradually  withdrawn 
from  the  cells  into  the  intercellular  spaces  where  the  ice  crystals 
are  gradually  formed.     This  is  in  reality  a  protection  to  the 
protoplasm,  since  it  becomes  "drier"  and  thus  more  resistant  to 
cold.     When  the  plants  "thaw"  out,  if  the  protoplasm  has  not 
been  killed  by  the  cold,  this  water  may  be  absorbed  by  the  proto- 
plasm again,  and  the  plant  is  not  injured.     Freezing,  then,  to  a 


FACTORS  OF  ENVIRONMENT. 


471 


certain  extent  has  the  same  effect  on  the  protoplasm  as  the  loss 
of  too  much  water  by  transpiration.  The  bud-scales  thus  pre- 
vent the  loss  of  too  much  water  from  the  cells  of  the  delicate 
tissues  of  the  growing  point  of  shoots  in  winter,  although  in 
many  cases  freezing  in  these  tissues  takes  place.  3d.  In  other 
cases  plants  are  killed  by  the  actual  freezing  of  the  protoplasm, 
though  there  are  some  plants  which  are  not  killed  by  freezing  of 
the  water  in  the  protoplasm.  The  ability  of  some  plants  to 
resist  this  is  probably  specific. 

914.  Wind. — The  effects  of  wind  on  vegetation  are  manifest 
in  several  ways  for  harm  or  for  good.     Severe,  frequent,  and 
long-continued    winds     stunt 

and  deform  trees  and  shrubs, 
and  destroy  or  reduce  the 
size  of  herbs.  Winds  also 
have  a  drying  effect,  and  this 
is  probably  one  of  the  reasons 
why  forests  are  not  developed 
on  much  of  the  prairie  re- 
gions. Every  now  and  then 
in  normally  humid  climates 
we  have  an  illustration  of  the 
blighting  effect  of  dry  winds 
on  vegetation.  "  Sand  blast," 
i.e.,  sand  driven  by  the  wind 
is  very  injurious  to  vegetation  Fl.g'  486' 

Mam  trunk   straight,  branches  all   bent 

in  sandy  areas  where  there  are  and  fixed  to  one  side  by  wind  from  one 

*  direction  (Rocky  Mountains). 

high  winds,  tearing  the  leaves 

and  even  eroding  the  shoots.  On  the  other  hand  wind  is  one  of 
the  great  agencies  for  pollination,  especially  in  the  case  of  ane- 
mophilous  plants,  and  it  is  one  of  the  important  agencies  for 
seed  distribution. 

915.  Ground  covers. — Plants  are  protected  by  the  covering 
of  the  ground  in  various  ways.     Among  the  lifeless  covers  may 
be  mentioned  the  following: 


472 


RELATION    TO  ENVIRONMENT. 


916.  Snow  cover.— Snow  protects  plants  during  the  winter  by 
checking  radiation  of  heat  from  the  soil  so  that  the  ground  does 
not  freeze,  or  freezes  to  a  less  depth.  For  trees  and  shrubs  this  is 
an  advantage,  since  root  absorption  is  permitted  to  some  extent, 
sufficient  often  to  supply  water  to  the  plant  which  is  lost  by  evap- 
oration from  the  branches  or  the  leaves  of  evergreens.  In  arc- 
tic and  alpine  regions  the  entire  vegetation  is  often  covered  and 
transpiration  thus  checked  in  the  cold  dry  atmosphere.  In 


Fig.  487. 
Snow  covering  showing  protection  of  low  vegetation  in  winter. 

these  regions  trees  and  shrubs  are  often  deformed  or  laid  pros- 
trate by  the  weight  of  snow,  so  that  it  exercises  a  dwarfing  influ- 
ence. That  snow  protects  trees  and  shrubs  from  dying  by  cov- 
ering them  up  is  shown  by  the  fact  that  in  arctic  regions  branches 
and  stems  projecting  above  the  snow  die  because  they  dry  out. 
In  temperate  regions  perennial  plants,  like  grass,  some  fall 
crops,  etc.,  are  protected  during  the  winter  by  snow  cover,  since 
a  more  equable  temperature  is  maintained  and  transpiration 
lessened.  Where  the  ground  is  bare  in  the  winter  the  alternate 
thawing  and  freezing  of  the  surface  "heaves"  the  ground  and 
lifts  the  roots  from  the  soil.  Snow  also  conserves  moisture  and 
distributes  snow-water  during  the  warm  season  in  mountain 
regions  over  a  longer  period,  especially  where  the  sun  does  not 


FACTORS  OF  ENVIRONMENT.  473 

have  such  a  direct  action  on  it.  Snow  and  ice  also,  in  the  form 
of  glaciers,  destroy  vegetation,  and  on  the  other  hand  grind  up 
rocks  and  assist  in  soil  formation. 

917.  Leaves  and  other  plant  remains  form  a  mulch  or  pro- 
tection cover,  which  is  especially  abundant  in  the  forest.     This 
protects  the  roots  from  extreme   cold,   lessens  radiation,   con- 
serves moisture,  etc. 

918.  Living  plant  covers. — The  highest  development  of  cover 
by  living  plants  is  seen  in  the  forest,  and  the  result  is  shown  in 
the  development  of  shade  plants  which  are  protected  from  ex- 
cessive light  and  heat,  while  the  air  of  the  forest  is  more  humid. 
The  under  plants  in  a  forest  are  also  provided  with  better  pro- 
tection from  cold.     The  water  from  rainfall  is  conserved,  and 
the  snow  melts  more  slowly,  thus  giving  a  more  uniform  distri- 
bution of  water  throughout  the  season  and  lessening  the  danger 
from  freshets  and  floods.     The  cushions  or  carpets  of  moss, 
formed   in   some   places,    conserve   moisture.     They   take   little 
moisture  from  the  ground,  since  the  moss  cushion  acts  some- 
thing like  a  sponge  to  absorb  and  hold  water  from  rainfall  or 
from  atmospheric  moisture. 

919.  Chemical  conditions  of  the  ground  or  water.— Chemical 
constituents  oj  soil.     The  chemical  constituents  of  the  soil  are 
derived  from  several  sources,  especially  from  solutions  of  eroded 
and  dissolved  rock  formations,  from  the  decaying  animal  and 
plant  remains,  from  certain  gases  taken  in  solution  in  rain-water, 
from  salts  of  sea-water,  etc.     Since  the  geological  formations  of 
the  earth  differ  in  their  constituents,  and  the  bulk  and  kinds  of 
plants  and  animal  remains  differ,  and  also  since  forces  of  erosion 
and  decay,  and  so  on,  vary  according  to  certain  conditions,  the 
soil  varies  greatly  over  the  face  of  the  earth  and  even  over  small 
areas.     According   to   investigations   on    certain   of   the   higher 
plants,   ten  elements  are  necessary  for  most  plant  growth,  as 
follows:    oxygen,   hydrogen,  carbon,   nitrogen,  phosphorus,   sul- 
phur, iron,  potassium,  calcium,  and  magnesium.     If  any  one  of 
these  is  lacking  in  suitable  quantity,  the  plants  become  sickly. 
For  most  green  plants,  most  of  the  carbon  and  much  of  the 


474  RELATION    TO   ENVIRONMENT. 

oxygen  come  from  the  CO2  of  the  air,  while  the  other  substances 
are  in  solution  in  the  soil,  or  in  certain  compounds,  or  are  brought 
into  solution  by  the  plant,  or  in  the  case  of  nitrogen  it  is  some- 
times fixed  from  the  air  by  microscopic  plants  and  made  avail- 
able for  plant  food.  There  are  other  substances  also  in  solu- 
tion in  the  soil,  and  plants  often  absorb  certain  substances  which 
are  not  needed  for  food,  and  sometimes  substances  which  are 
harmful. 

920.  Effect  on  plants. — Whenever  one  or  more  of  these  ele- 
ments are  in  excess  in  the  soil,  or  where  harmful  substances  are 
in  solution  in  perceptible  quantities,  the  vegetation  responds  by 
changes,  by  varying  in  vigor  of  growth,  or  a  varying  ratio  be- 
tween growth  and  reproduction,  or  by  a  modification  of  the  habit, 
form,  structure,  and  function.  The  most  marked  modifications 
induced  by  chemical  conditions  of  the  soil  are  in  the  case  of  the 
alkaline  or  salt  basins,  the  excess  of  salt  interfering  with  root- 
absorption,  resulting  in  a  modification  of  stem  and  leaf  by  reduc- 
tion of  transpiration  surface,  and  increase  of  water-storage 
tissue.  Similar  modifications  also  take  place  in  plants  grow- 
ing in  peat  moors,  where  there  is  an  abundance  of  humus  acid  in 
the  soil.  Soils  with  an  abundance  of  lime  also  influence  certain 
vegetation,  modifying  in  some  cases  certain  species  so  that  they 
take  an  alpine  form.  The  chemical  condition  of  the  soil  is 
directly  related  to  the  plant's  ability  to  absorb  water.  The 
roots  of  plants  will  absorb  more  water  when  pure  than  when  it  is 
in  solution.  For  absorbing  nutrient  salts  for  every  plant  there 
is  a  most  favorable  concentration,  above  which  they  take  up 
water  with  difficulty.  (The  concentration  of  the  solution  which 
plants  can  take  up  rarely  exceeds  3  per  cent,  and  in  most  land 
plants  is  far  below  this.)  Different  kinds  of  salt  solutions  affect 
in  a  different  degree  the  absorption  activity  of  the  plant,  for 
example,  sodium  chloride  (table  salt)  acts  more  energetically  in 
retarding  absorption  than  sodium  nitrate  (saltpeter).  Mixing 
of  different  salts  acts  more  energetically  than  a  single  salt. 

The  mineral  substances  in  the  soil,  as  nitrates,  phosphates, 
sulphates,  lime,  potash,  magnesium,  and  iron  oxide,  are  impor- 


FACTORS  OF  ENVIRONMENT.  475 

tant,  not  only  because  of  the  effect  they  have  upon  the  physical 
condition  of  the  soil,  but  also  because  of  their  activity  in  the 
various  metabolic  processes  in  the  plant.  Some  enter  into  the 
production  of  protoplasm,  some  play  a  secondary  part  in  stimu- 
lating certain  processes  or  activities  of  the  plant. 

Within  certain  limits  plants,  adapt  themselves  to  changes  in 
the  chemical  condition  of  the  soil,  or  to  chemically  different 
soils,  but  there  is  great  variation  in  this  respect  in  different 
species.  To  a  nutriment  salt  like  sodium  nitrate  in  the  soil, 
plants  will  adapt  themselves  more  readily  to  an  increase  in  the 
concentration,  than  to  a  non-nutrient  salt  like  sodium  chloride. 
But  when  the  concentration  of  the  salt  goes  beyond  a  certain 
grade,  according  to  the  species,  it  acts  as  a  poison. 

921.  Physical  condition  of  soil.— Rocky  regions  are  least 
suited  for  vegetation,  except  under  certain  conditions,  and  with 
a  limited  number  of  plants.  In  mountain  regions,  large  areas 
of  rock  may  be  bare  of  vegetation,  especially  if  the  rock  lacks 
crevices.  In  the  drier  situations  the  vegetation  may  be  limited 
to  rude  lichens,  or  a  few  of  the  lower  algae  in  moist  situations. 
Along  the  sea-coast,  where  the  rocks  are  washed  by  wave 
action,  certain  of  the  large  marine  algae  are  enabled  to  obtain 
a  foothold  by  means  of  holdfasts,  even  on  the  smooth  surface 
of  rocks. 

Where  the  rocks  are  creviced,  there  is  an  opportunity  for  foot- 
hold for  a  greater  variety  of  plants,  mosses,  ferns,  and  the  flow- 
ering plants.  The  crevices  also  serve  to  catch  and  retain  the 
disintegrating  remains  of  lichens  and  other  vegetation  which 
mingle  with  the  crumbling  portions  of  rock,  and  form  a  different 
soil  which  provides  food  for  a  greater  variety  of  plants.  Where 
the  rock  is  more  broken  in  the  form  of  boulders  or  small  stones, 
the  more  exposed  surfaces  harbor  lichens,  while  the  interstices 
give  an  opportunity  for  the  accumulation  of  a  greater  mass  of 
finer  soil.  Where  the  rock  is  reduced  to  gravel  or  coarse  sand, 
the  disintegrating  vegetation  eventually  mixes  with  and  covers 
it,  offering  a  still  wider  range  for  plant  growth.  With  the 
weathering  and  crumbling  of  the  rocks,  the  admixture  of  decay- 


RELATION   TO  ENVIRONMENT. 

ing  vegetation,  and  the  action  of  certain  chemical  solvents  on 
certain  rocks,  the  finer  and  less  porous  soils  are  formed.  The 
variation  in  the  proportion  of  these  ingredients  together  with  the 
different  degrees  of  disintegration  of  vegetable  matter  make  the 
soils  of  different  physical  conditions. 

922.  Relation  of  physical  condition  of  soil  to  plant  growth. — 
The  relation  of  these  different  physical  conditions  of  soil  to  plant 
growth  lies  in  the  means  it  affords  the  plant  to  get  and  maintain  a 
foothold,  its  power  of  absorption  and  retention  of  water,  the  cir- 
culation of  air,  the  ability  with  which  the  soil  particles  hold 
mineral  substances  necessary  for  plant  food,  its  power  to  absorb 
or  radiate  heat,  to  reflect  or  absorb  light,  its  tenacity  or  power  of 
resistance  to  washing  by  heavy  rains,  or  drifting  in  winds,  etc. 
Thus  the  soils  of  a  region  having  the  same  annual  rainfall  vary 
in  their  capacity  to  hold  water,  so  that  one  kind  of  soil  may  have 
a  vegetation  which  is  largely  xerophytic  (see  Chapter  XLVII); 
for  example,  fine  ground  lime  soil  poor  in  humus,  because  of  its 
low  water-holding  power,  while  on  lime  soil  rich  in  humus  a 
mesophytic  or  hydrophytic  vegetation  may  thrive.     Sand  has  a 
less  water  capacity  than  clay,  and  also  parts  with  it  much  more 
readily  by  evaporation.     A  fine-grained  soil,  rich  in  humus,  is 
most  favorable  for  the  retention  of  a  suitable  amount  of  moisture. 
Forests   and   meadows   here   reach   their   highest   development. 
Sandy  soil  poor  in  humus  underlaid  with  gravel  becomes  wet 
with  each  rain,  but  quickly  dries  out.     Clay  surpasses  all  soils  in 
its  power  to  take  up  and  retain  water.     According  to  Schimper, 
clay  grounds  in  the  dry  regions  of  the  Mediterranean  are  highly 
prized  because  of  this  power  to  absorb  and  hold  water,  while  in 
west  Europe  where  the  precipitation  is  great,  the  clay  soils  are 
often  too  wet.     In  this  condition,  clay  soils,  as  well  as  lime  soils 
rich  in  humus,  are  apt  to  lack  oxygen  because  of  their  non- 
porous  condition,  and  are,  therefore,  unfavorable  for  plant  growth. 

923.  The  chemical  condition  of  the  soil  often  affects  its 
physical  properties,  so  that  clay  is  made  less  porous  by  adding 
potash,  ammonia,  etc.,  or  more  porous  by  the  addition  of  certain 
acid  salts,  phosphoric  acid,  etc. 


FACTORS   OF  ENVIRONMENT.  477 

II.  Climatic  Factors. 

924.  Rainfall,  or  precipitation.— This  factor  has  a  close  rela- 
tion to  the  water  factor,  but  still  its  effect  in  general  is  climatic. 
Rainfall  is  one  of  the  most  important  elements  determining  the 
plant  population  of  a  region.     The  luxuriance  of  vegetation  and 
the  number  of  individuals  of  a  kind,  other  things  being   equal, 
is  in  direct  relation  to  the  percentage  of  rainfall  over  different 
parts  of  the  earth's  land  surface.     Rainfall  depends  on  currents 
of  moisture-laden  air  from  warm  bodies  of  water  sweeping  over 
cooler  areas  of  water  or  land,  or  more  rarely,  on  currents  of  cool 
air  passing   over   warm   areas   covered   with   a   moisture-laden 
atmosphere.     According   to    scarcity   or   abundance   of   rainfall 
the  earth  may  be  mapped  into  areas  of  rich  vegetation,  largely 
forest  areas;    into  plains  or  steppes;    prairies;    and  deserts  (see 
Chapter  XLIX).     It  will  be  well  to  note  here  briefly  the  rainfall 
or  precipitation  in  different  parts  of  the  earth. 

925.  In  North  America,  a  narrow  belt  along  the  Pacific  in  Oregon  and 
Washington,  the  rainfall  is  more  than  60  inches  annually.     In  some  places 
in  Washington  State  it  is  more  than  100  inches.     This  is  due  to  the  mois- 
ture-laden  winds  from  the  warm  waters  of  the  Pacific   Ocean  coming 
in  contact  with  the  cooler  air  of  the  land.     In  Florida  there  are  similar 
abundant  rains,  owing  to  the  warm  winds  from  the  tropical  seas.     For 
the  same  reason  the  annual  rainfall  in  the  Gulf  and  Atlantic  States  is 
in  general  more  than  50  inches.     The  luxuriance  of  vegetation  in  some 
parts  of  Florida  and  Washington  is  found  where  the  rainfall  is  so  great. 

926.  The  great  arid  region  of  the  United  States. — There  is  a  district 
in  Nevada,  southern  California,  and  Arizona  where  the  annual  rainfall  is 
less  than  5  inches,  while  in  most  of  Nevada  and  Utah,  parts  of  Arizona, 
New  Mexico,  Colorado,  and  Wyoming  it  is  below  10  inches.    The  Sonora- 
Nevada  Desert  is  located  in  this  region.     A  wider  belt  extends  from  middle 
Oregon  far  into  Nebraska  and  South  Dakota,  where  the  precipitation  is 
less  than  20  inches.     The  warm  moisture-laden  winds  of  the  Pacific  lose 
a  large  part  of  their  moisture  near   the   coast,  move  eastward  over  the 
Rocky  Mountains,  and  furnish  comparatively  little  rainfall  from  middle 
Oregon   eastward.      The    Rocky   Mountains,    being   so   high    and    cold, 
cause  a  greater  precipitation  of  the  small  amount  of  moisture  remain- 
ing in  the  air  than  occurs  on  other  plateaus  (Gilbert  and  Brigham,  Intro- 
duction, Phys.  Geog.).    The  northern  Mississippi  region  receives  a  medium 
amount  of  rain   from   the  diminishing   moisture-laden   atmosphere   from 


RELATION    TO   ENVIRONMENT. 

the  Gulf  and  Middle  Atlantic,  yet  it  is  still  sufficient  to  support  an  abun- 
dance of  plant  life.  Thus  it  is  seen  that  in  general  the  interior  of  continents 
is  drier  than  the  coast  regions. 

927.  In   southern  California,   Lower  California,   and   northern   Mexico 
the  arid  region  extends  to  the  Pacific,  since  the  warmth  of  the  land  is  not 
sufficient  to  cause  precipitation  of  the  cooler  air  at  this  point. 

928.  In  Central  America,  northern,  central,  and  eastern  parts  of  South 
America,  the  rainfall  is  very  great.     This  constitutes  the  humid  tropical 
region  of  the  western  continents,  which  is  noted  for  the  luxuriance  of  its 
vegetation.      In  much  of  the   Amazon  country  the  rainfall  is  over  80 
inches.     The  prevailing  winds  are  here  from  the  very  warmest  part  of 
the  Atlantic  Ocean,  which  explains  the  exceptional  precipitation  in  this 
continental  interior.     West  of  the  Andes  mountain  range  it  is  dry. 

929.  In  Great  Britain  the  warm  Atlantic  currents  furnish  warm,  moist 
winds  which  on  the  west  coast  give  a  precipitation  of  about  40  inches, 
while  in  the  cooler  highlands  it  reaches  60  to  80  inches,  and  falls  to  25 
to  30  inches  on  the  east  coast.     The  latter  is  low  for  plants,  but  is  ample 
in  such  a  cool  climate  as  that  of  England.     In  southern  Europe  the  rain- 
fall is  gradually  less  toward  the  interior  of  the  continent. 

930.  Much  of  Russia  and  Siberia  is  arid,  especially  northeast  Russia 
(the  interior  from  east  to  west).     The  prevailing  winds  are  from  the  cold 
Arctic  Ocean,  which  passing  over  a  warmer  land  area,   the  moisture  is 
only  slightly  precipitated.     In  southern  Siberia  there  is  moderate  rainfall. 

931.  India  and  Burma  are  furnished  with  a  high  annual  rainfall  because 
of  their  relation  to  the  warm  Indian  Ocean  to  the  south,  from  which  the 
prevailing  winds  sweep  with  great  force  from  the  southwest  and  are  called 
monsoons.    These  produce  great  rains  over  southern  Asia  to  the  Himalaya 
Mountains,  at  which  point  most  of  the  moisture  has  been  precipitated. 
In  the  delta  region  of  the  Ganges  River  the  monsoon  winds  from  the  Indian 
Ocean  yield  the  highest  precipitation,  the  annual  rainfall  being  over  500 
inches,  or  in  one  year  over  800  inches,  equals  67  feet.      The  luxuriance 
of  the  vegetation  of  southern  Asia  is  well  known.     On  the  other  hand, 
the  high  plains  of  Tibet  and  Central  Asia  just  beyond  the  Himalayas  are 
arid,  and  have  a  desert  vegetation. 

932.  In  eastern  Asia  there  is  a  plentiful  rainfall.      In  Japan  the  rainy 
season  extends  from  April  to  September,  and  at  Tokio  the  annual  rain- 
fall is  about  58  inches.      In  Korea  it  is  36  inches.      Hongkong,  farther 
south,  has  a  rainfall  of  78  inches,  while  in  the  Philippine  Islands  and  Dutch 
East  Indies  the  winds  coming  from  the  warm  parts  of  the  Pacific  product 
great  rainfall. 

93  .  In  Australia  in  the  central  west  the  precipitation  is  less  than  e 
inches;  in  the  lower  part  of  the  interior  it  is  about  10  inches;  but  is  heaviei 
toward  the  east  coast  and  over  a  small  area  on  the  southwest  coast. 


FACTORS   OF  ENVIRONMENT.  479 

934.  In  the  Sahara  Desert  the  winds  come  mainly  from  the  cool  Medi- 
terranean at  the  north,  so  that  there  is  little  or  no  precipitation. 

935.  Temperature. — Besides  the  physical  effects  of  heat,  heat 
is  to  be  considered  as  a  climatic  factor.     The  amount  of  heat 
during  the  period  of  growth  and  reproduction  has  a  very  im- 
portant bearing  on  the  limits  of  plant  distribution.     Plants  vary 
in  their  total  heat  requirement,  so  they  are  drawn  into  broad 
climatic  zones,  from  polar  lands  to  the  equator  and  also  more  or 
less  parallel  with  mountain  chains.     Ocean  currents  affect  the 
climate,  and  also  deflect  these  life  zones,  as  they  are  called  (see 
Chapter  XLVIII).     "Glacial"  epochs  also  profoundly  influenced 
the  vegetation  of  the  earth,  since  the  southward  extension  of  the  cold 
wave  was  so  great  as  to  destroy  plant  life  over  large  regions,  and 
cause  a  general  southward  shifting  of  the  life  zones  which  moved 
northward  again  as  the  glaciers  retreated  (see  Chapter  XLVIII). 

936.  Physiography.— The    physiography  of   the  earth's  sur- 
face  exerts   a   powerful   influence   upon   vegetation.     Mountain 
chains,  oceans,  rivers,  etc.,  present  barriers  to  plant  migration. 
They  also  produce  lines  of  tension  or  stress  between  them  and 
adjacent  territory.     Rivers  also  act  as  conductive  agencies.     On 
mountain  sides  lines  of  stress  are  also  produced  because  of  dif- 
ference in  altitude,  and  consequently  difference  in  temperature, 
so  that  a  zonal  arrangement  of  vegetation  results.      Thus  the 
life  zones  which  are  in  general  transcontinental  are  deflected  far 
to  the  south  or  north  because  of  variations  in  temperature  accom- 
panying variations  in  altitude,  or  influenced  by  the  different  ocean 
currents.     In  hilly  countries,  as  well  as  in  mountains,  exposure 
to  light,  the  sun's  heat,  etc.,  affects  vegetation,  while  the  undu- 
lating surface  is  one   of  the  factors  in  determining  the  water 
content  of  the  soil. 

HI.  Biotic  Factors. 

937.  Factors  for  pollination  and  distribution. — Some  of  the 
biotic  factors  have  been  discussed  in  other  places.     The  agency  of 
insects  in  pollination,  in  the  case  of  entomophilous  flowers  in  Chap- 
ter XLIII,  has  a  great  influence  in  increasing  the  fertility  and 


480  RELATION  TO  ENVIRONMENT. 

vigor  of  many  plants.  Birds  and  other  animals  aid  in  distribu- 
tion by  eating  fruit  and  seeds,  many  of  the  seeds  being  evacu- 
ated unharmed,  while  in  some  seeds  their  germinating  power  is 
increased  by  passage  through  the  alimentary  canal  of  animals. 
Squirrels  bury  nuts,  many  of  which  are  forgotten,  and  are  thus 
in  a  condition  to  germinate.  Some  animals  carry  in  their  hair 
or  fur  seeds  which  are  provided  with  grappling  appendages. 
The  various  mechanical  adaptations  for  pollination  and  seed 
distribution,  the  various  means  for  protection,  might  also  be 
mentioned. 

938.  Factors   changing  the  soil.— Burrowing  animals  bring 
about  a  rude  sort  of  accidental  culture,  perhaps  giving  rise  in  the 
past  to  certain  weed  types.     Certain  ants  cultivate  grains  for 
food.     Of  the  greatest  importance  to  vegetation  is  the  burrowing 
work  of  earthworms,  since  they  loosen  up  heavy  soils,  permit 
access  of  air,  of  humus,  and  often  make  it  possible  for  roots  to 
penetrate  into  compact  soils.     When  they  come  to  the  surface 
their  earthy  excrement  covers  leaves  and  assists  in  decay,  while 
the  alkaline  excretions  of  their  bodies  neutralize  to  some  extent 
the  humic  acid  in  the  woods.     Man  in  his  cultural  operations 
has  profoundly  changed  the  face  of  nature, — produces  immense 
crops  of  certain  useful  plants,  and,  by  taking  advantage  of  a 
knowledge  of  laws  of  evolution,  is  turning  his  attention  to  guiding 
evolution  of  more  useful  plants. 

939.  The  active  factor  in  plants.— Plants  themselves  are  im- 
portant biotic  factors  influencing  vegetation.     The  shade  of  the 
forest,  or  of  other  layered  plant  societies,  protects  vast  numbers 
of  plants,  gives  protection  to  vast  numbers  of  climbers,  epiphytes, 
etc.,  while  all  are  apt  to  harbor  parasites  when  living,  but  cer- 
tainly are  the  prey  of  the  scavenger  members  when  dead.     These 
immensely  important  members  of  all  plant  societies  reduce  dead 
vegetation  to  humus,  and  eventually  to  a  condition  in  which  it  is 
again  available  for  food  for  the  higher  plants.     In  this  phase  of 
the  work  the  lower  organisms  often  join  forces  with  the  roots  of 
the  higher  plants  in  symbiosis  or  mutualism.     Then  there  are 
the  bacteria  which  fix  nitrogen,  the  legume  tubercle  organism, 


FACTORS  OF  ENVIRONMENT.  481 

the  nitrate  and  nitrite  bacteria,  etc.,  which  prepare  food  for  the 
higher  plants. 

940.  The  responsive  factor  in  plants. — The  power  which  the 
plant  possesses  to  relate  itself  to  environment,  and  to  undergo 
slight  changes  in  form,  texture,  etc.,  which  adapt  it  better  to 


Fig.  4870. 
Willow  trees  pollarded  by  man 


different  conditions,  is  a  most  important  factor.  This  is  shown  in 
the  power  of  growth  and  response  to  environment  in  the  assump- 
tion of  favorable  positions  by  its  different  parts  from  the  seedling 
stage  onward.  This  response  of  plants  to  environment  is  further 
manifested  in  the  diurnal  and  nocturnal  movement  of  leaves,  the 
nutation  of  stems,  etc. 


CHAPTER  XLVII. 

VEGETATION  TYPES  AND  STRUCTURES. 

941.  By  vegetation  type  is  meant  the  form  and  character  of 
vegetation   elements   under   special   conditions   of   environment. 
We  are  concerned  primarily  with  a  study  of  the  plant  form  as 
related  to  environment,  not  with  a  study  of  floral^ Cements  or 
plant  relationships.     Species  which  are  not  at  all  cldfely  related 
from  a  taxonomic  standpoint  may  be  of  the  same  vegetation 
type. 

942.  The  responsive  type  of  vegetation. — By  this  is  meant  tlie 
reaction  of  vegetation  to  environment,  the  response  of  the  plant 
in   adapting   itself   to   its   environment.     Within   certain   limits 
many  plants  will  respond  in  a  single  season  to  a  change  of  envi- 
ronment and  will  assume  a  form  of  leaf  and  stem  which  fits  them 
to   better   endure   the   unfavorable   conditions.     This,  however, 
takes  place  where  the  change  is  not  very  great,  or  in  case  of  cer- 
tain plants  which  have  a  wide  range  of  adaptability.     Vegetation 
types   have   been   developed   by   gradual   change   through   long 
periods  of  time.     Some  of  the  striking  vegetation  types  are  those 
of  desert  plants,  those  growing  in  sandy  areas  in  moist  climates, 
or  where  the  soil  is  very  alkaline  and  interferes  with  absorption. 
The  types  found  in  these  situations  are  similar,  since  the  plants 
obtain  water  with  difficulty  from  the  soil,  and  so  their  aerial  parts 
in  response  to  this  take  on  a  form  which  enables  them  to  con- 
serve water.     There  are  several  different  classifications  of  vege- 
tation types.     Two  of  these,  proposed  by  Warming  and  Schim- 

482 


VEGETATION   TYPES.  483 

per,  will  be  presented  here.     These  vegetation  types  are  classified 
into  societies  as  follows: 


I.  Warming's  Vegetation  Types. 

943.  Mesophytes. — These    are    represented    by   land   plants 
under  temperate  or  medium  climatic  and  soil  conditions.     The 
north  temperate  regions  (with  the  exception  of  mountain  heights, 
the  arid  regions,  the  sand-dune  areas,  etc.)  are  most  favorable 
for  the  development  of  the  mesophyte  type.     The  normal  land 
vegetation  of  our  temperate  region  is  composed  of  mesophytes; 
example,  the  deciduous  forests  or  thickets  of  trees  and   shrubs 
with   their  undergrowth,   the   meadows,   pastures,   and  prairies. 
Mesophytes  occur,  however,  in  arctic  regions;  for  example,  the 
low-growing    mats    of   grass,    or    herbaceous    vegetation    which 
appears  during  the  summer  months.     The  rainy-season  flora  of 
the  deserts  or  plains  also  forms  mesophytic  societies.     The  land 
of  these  regions,  however,  is  not  populated  by  mesophytes  alone. 
There  are  many  xerophytic  plants  growing  in  mesophytic  soci- 
eties;  for  example,  the  conifers  in  the  "mixed"  forests  are  xero- 
phytes,  and  make  the  characteristic  xerophytic  society  of  sub- 
arctic or  subalpine  regions.     There  are  many  other  examples  of 
xerophytic  plants  growing  in  mesophytic  societies,  as  the  purslane 
(Portulaca),  the  stonecrops  (Sedum),  some  of  the  cacti,  etc. 

944.  Xerophytes. — Plants    growing    in   very  dry    regions,  or 
under  conditions  of  environment  where  absorption  of  water  by 
the  roots  is  difficult,  or  such  as  to  favor  the  loss  of  water  from 
the   aerial   organs   in   excessive   amounts   for   long   periods,   are 
known   as   xerophytes.     A   plant    having   a   habit   or   structure 
which  fits  it  to  live  under  these  extreme  conditions  is  a  xerophyte. 
The   most   characteristic    xerophytic  plants  are   the    perennials 
which   inhabit   the   desert.     Less   highly   specialized   xerophytes 
are  those  which  grow  in  subarctic  or  alpine  regions,  or  in  rocky 
places  or  on  sand-dunes.      In  the  deserts  especially,  xerophytic 
plants  are  developed  to  the  exclusion  of  others,  except  in  certain 
specially  favored   localities,  and  excepting  also  the  rainy-season 


484  RELATION   TO  ENVIRONMENT. 

flora.  In  subarctic  and  alpine  regions,  as  well  as  in  rocky 
places  or  in  sand-hills,  mesophytic  plants  are  often  intermingled, 
because  the  conditions  of  environment  are  not  so  austere.  Xero- 
phytic  situations  are  as  follows: 

1.  Deserts,  sand    and  gravel   hills,  sand-dunes,  rocky  places, 
steppes  and  some  prairies,  high  arctic  and  alpine  districts. 

2.  Soils  or  waters  with  large  quantities  of  acids  (as  humic  acid 
in  certain  marshes  or  woods),  or  of  salts  (brackish  or  salt  marshes 
or  bodies  of  water,  and  alkaline  soils). 

945.  Hydrophytes. — Plants  growing  in  "fresh"  water,  or  in 
land  where  the  soil  is  very  wet,  or  the  air  very  humid  throughout 
the  season,  are  hydrophytes.     They  have  a  water  environment,  or 
one  in  which  the  air  is  so  moist  that  loss  of  water  from  the  aerial 
organs  is  hindered.     The  leaves,  and  often  the  stems,  even  of 
land  hydrophytes,  are  soft  and  watery.     They  favor  rapid  loss  of 
water,  but  the  moist  environment  checks  the  too  rapid  transpira- 
tion. 

946.  Halophytes. — It  is  customary  to  restrict  the  term  hydro- 
phytes to  plants  growing  in  bodies  of  "fresh"  water.     Plants  in 
salt  or  brackish  water  are  halophytes.     Halophytes  differ  from 
hydrophytes  in  the  fact  that  the  protoplasm  of  the  former  has  a 
higher  osmotic  tension  than  the  latter.     Halophytes  are  there- 
fore enabled  to  live  in  saline  water  and  to  absorb  liquid  food  from 
the  same.     The  usual  hydrophytes,  placed  in  the  same  environ- 
ment, would  collapse,  because  not  only  could    they  not  absorb 
water,  they  would  lose  their  turgor  and  collapse  because  of  the 
higher  osmotic  tension  of  the  water  environment.     Those  halo- 
phytes which  are  rooted  in  soil  saturated  or  covered  with  salt 
water  (salt-marsh  plants),  and  have  aerial  organs  for  transpira- 
tion, have  a  xerophytic  habit  so  far  as  their  leaves  or  aerial  parts 
are  concerned.     In  fact  they  are  by  some  classed  with  xero- 
phytes.     This  is  because  the  salinity  of  the  water  retards  root 
absorption,  and,  in  correlation  with  this,  the  aerial  parts  have 
taken  on  a  xerophytic  habit  in  order  to  retard  transpiration. 
Halophytes,  however,  which  are  habitually  immersed  in  water, 
as  the  seaweeds  for  example,  cannot  be  considered  as  xerophytes. 


VEGETATION    TYPES. 


485 


II.  Schimper's  Vegetation  Types. 

947.  Another  general  classification  of  plants  as  regards  their 
adaptation  to  environment  is  that  proposed  by  Schimper.     There 
are  three  kinds: 

1.  Hygrophytes,  which  are  especially  provided  with  structures 
favoring  the  loss  of  water,  and  which  usually  live  under  condi- 
tions in  which  the  danger  of  desiccation  is  excluded. 

2.  Xerophytes,  or  dry-conditioned  plants,  which  exist  under 
conditions  which  necessitate  specialized  structures  for  conserving 
water  and  for  retarding  transpiration. 

3.  Tropophytes. — These 
are  plants  which    corre- 
spond   nearly    with    the 
mesophytes  of  the  former 
classification.   They  show 
a  remarkable  adaptation 
to  extreme  conditions,  and 
represent      the      highest 
physiological  type  of  tem- 
perate-region plants. 

948.  Tropophytes.  — 
Several   types  of    tropo- 
phytes  are  recognized. 

i.  Deciduous  trees  and 
shrubs.  —  Through  the 
growing  season  these 
plants  bear  foliage.  The 
transpiration  stream  is 
strong,  root  absorption  is 
active,  and  transpiration 
is  abundant.  The  plants 
in  this  condition  are 
mesophytes,  and  their  life  perennial  plant  (J^nt!Lulis)  with  a  subter- 

relations     are     temperate,      raneanrootstock,  and  annual  leaf  and  flower 

With  the  approach  of  winter  they  shed  their  leaves  and  thus  turn 


486  RELATION   TO   ENVIRONMENT. 

from  a  mesophytic  to  a  xerophytic  habit.  If  the  usual  broad- 
leaved  trees  and  shrubs  retained  their  green  living  leaves  through 
the  winter,  the  loss  of  water  would  be  so  great  as  to  kill  the 
trees.  The  soil  being  so  cold,  root  absorption  is  at  a  very 
low  ebb,  or  often  ceases  for  considerable  periods.  By  discarding 
their  leaves,  transpiration  is  greatly  lessened,  and  the  life  of  the 
tree  or  shrub  is  preserved. 

2.  Perennial  herbaceous   plants. — In    these   plants   the    aerial 
shoots  as  well  as  the  leaves  usually  die  on  the  approach  of  winter, 
while  the  underground  shoot,  in  the  form  of  a  bulb,  tuber,  rhi- 
zome, or  simple  shoot-stem,  is  protected  from  drying  out  by  its 
covering  of  soil  or  leaf-mold.     These  plants  are  sometimes  termed 
glophilous,  because  they  are  dependent  on  the  subterranean  parts 
for  preservation  through  the  winter. 

3.  The  annuals  and  biennials  might  be  treated  of  as  a  third 
type  of  tropophytes.     In  the  annuals  the  plant  lives  only  through 
the  growing  season,  and  on  the  approach  of  winter,  or  of  the 
period    when    extreme   xerophytic    conditions   prevail,    turns    to 
seed.     The  seed  is  the  xerophytic  stage  of  the  plant.     Biennials 
might  even  be  made  a  fourth  type,  the  underground  stem  being 
developed  the  first  year,  exists  through  the  winter,  and  the  sec- 
ond year  the  plant  forms  seed. 

III.  Plant  Structures  Adapted  to  Conditions  of 
Environment. 

949.  The  normal  plant  condition. — Theoretically  the  normal 
plant  condition  is  one  in  which  the  plant  lives  under  uniform 
conditions  of  environment  throughout  the  year,  with  slight 
fluctuations  of  temperature,  humidity  of  the  air,  etc.  These 
conditions  are  more  nearly  approximated  in  humid  tropical 
countries.  Temperature  and  moisture  conditions,  both  of  soil 
and  air,  are  relatively  high  and  uniform.  These  conditions 
favor  luxuriant  vegetation,  which  is  characteristic  of  the  humid 
tropics.  Many  tropical  plants,  like  the  palms,  are  evergreen, 
because  they  hold  their  leaves  for  more  than  one  year.  But 


VEGETATION   TYPES.  487 

many  other  tropical  plants  are  deciduous,  casting  their  leaves 
simultaneously,  and  in  a  few  days  new  leaves  are  put  forth. 
There  are  no  periodic  extremes  which  require  xerophytic  struc- 
tures for  a  season.  Under  these  normal  static  conditions  for 
plant  growth,  we  would  expect  a  luxuriant  development  and  a 
vast  overproduction  with  a  tendency  to  migrate  outward  into 
subtropic  and  temperate  regions,  during  which  modifications 
are  slowly  brought  about  in  the  evolution  of  species  adapted  to 
different  conditions.  Under  these  normal  uniform  conditions 
the  plant  develops  an  extensive  foliage  surface  adapted  to  trans- 
piration, which  is  not  likely  to  become  excessive  because  of  the 
high  degree  of  humidity  of  the  air  as  well  as  the  abundant  pre- 
cipitation. 

950.  Xerophytic  structures. — The  physical  factors  which  de- 
termine the  conditions  for  xerophytic  vegetation  are  of  two  kinds: 

1.  Those  which  decrease  the  water  supply  to  the  plant,  or  make 
it  very  limited,  as  slight  precipitation,  porous  soil  of  a  texture 
which  does  not  readily  hold  water,  lack  of  subterranean  supply, 
or  "ground  water,"  strong  winds  or  continual  sunshine,  which 
dry  out  the  soil,  low  temperature,  thin  soil  covering  on  rock  sub- 
soil, thin  mulching  of  vegetation,  steepness  of  slope  which  ad- 
mits of  rapid  removal  of  water. 

2.  Those  which  accelerate  the  loss  oj  water  from  the  plant,  as 
dry  air,  high  winds,  high  temperature  if  accompanied  by  dry- 
ness    of    air,    low    atmospheric    pressure,    intense    illumination, 
absence   of   tall   vegetation   which   affords   protection   to   shade 
plants. 

In  the  adaptation  of  plants  to  dry  conditions  modifications 
have  taken  place  along  many  different  lines.  These  modifica- 
tions are  all  designed  for  the  same  purpose,  to  conserve  water 
for  the  plant,  to  increase  absorption  by  the  roots,  and  to  decrease 
transpiration  by  the  aerial  parts. 

951.  Lessened  transpiration.— This  is  brought  about  in  thf 
case  of  xerophytic  plants  in  four  general  ways: 

i.  Reduction  oj  leaf  surface.— This  is  usually  accompanied  by 
a  thickening  of  the  leaf,  so  that  for  the  same  mass  of  leaf  sub- 


488 


RELATION   TO   ENVIRONMENT. 


stance  there  is  a  less  surface  for  transpiration.  The  needle-like 
or  awl-shaped  leaves  of  the  conifers,  junipers,  etc.,  are  examples 
of  xerophytic  structures  adapted  to  lessen  transpiration.  The 
leaves  of  yuccas,  while  quite  large,  are  very  narrow  and  pointed  in 
proportion  to  the  mass  of  the  leaf.  This  kind  of  leaf  is  charac- 
teristic of  many  plants  of  deserts  or  permanently  arid  regions. 
Examples  need  not  be  multiplied  here ;  some  are  mentioned  under 
the  general  treatment  of  leaves  (Chapter  XL),  and  others  in 
treating  of  desert,  arctic,  heath,  salt-marsh,  and  other  societies. 
Periodic  and  complete  reduction  of  leaf  surface  takes  place  in 
tropophytic  plants  in  preparing  them  for  the  xerophytic  stage 
in  which  they  pass  the  winter  (see  paragraph  938). 

.2.  By  protective  covering  or  movements. — Protective  coverings 
in  the  form  of  hairs,  scales,  a  more  or  less  thickened  cuticle, 
thickening  of  the  epidermal  wall,  or  a  doubling  of  the  epidermal 
layers  retard  the  loss  of  water.  Protective  movements  of  leaves 
also  take  place  in  some  plants,  which  tends  to  lessen  transpira- 
tion. A  slight  loss  of  turgor  often  causes  leaves  to  droop  and 
assume  a  position  in  which  transpiration  is  lessened.  Remark- 
able movements  of  leaves  take  place  in  the  so-called  sensitive 
plants,  belonging  to  the  acacias  and  mimosas.  These  are  highly 
developed  in  arid  regions.  When  the  loss  of  water  passes  the 
optimum,  the  leaflets  fold  together,  or  the  whole  leaf  droops  and 

brings  the  leaflets  in  close 
approximation  which  retards 
transpiration.  The  leaves  of 
many  grasses  become  rolled 
up  and  thus  lessen  the  loss 
of  water.  The  leaves  of  the 
evergreen  rhododendrons  roll 
up  in  a  striking  way  when 
the  loss  of  water  becomes 
Fi  g  excessive  in  drought,  but  es- 

Deeply  sunken  stoma  of  Franklandia  peciallv  in  Very  cold  Weather, 
fucifolia.  (After  Schimper.)  * 

3.  Action   ana  position    o] 
the  stomata. — The  work  of  the  stomata  in  regulating  transpira- 


VEGETATION   TYPES.  489 

tion  has  been  described  (paragraph  84).  In  many  xerophytic 
plants,  especially  in  arid  regions,  the  stomata  are  sunk  in  deep 
cavities  in  the  leaf  so  that  the  loss  of  water  from  them  is  not 
so  rapid.  In  many  cases  several  of  the  above  types  of  means 
for  retarding  the  loss  of  water  from  leaves  are  combined. 

4.  Total  absence  of  foliage  leaves. — This  is  a  striking  pecu- 
liarity of  many   desert  plants,  or  plants  of  very  arid  regions, 
for  example  the  cacti.      Even  in  regions  where  mesophytes  and 
hydrophytes  grow  there  are  examples  of  plants  devoid  of  leaves, 
as  seen  in  the  horsetails  and  in  many  of  the  rushes. 

5.  Thorns  and  spines. — With   the  reduction  of  leaves  there 
often  occurs  a  development  of  thorns  and  spines,  especially  in 
dry  situations.     These  often  accompany  reduced  leaves  on  the 
same  plant,  while  in  the  cacti  the  spines  often  take  the  position  of 
leaves. 

6.  Wafer  reservoirs. — In   some   plants  the  power  of  holding 
considerable  amounts  of  water  in  their  tissues  is  very  marked. 
Such  parts  of  the  plant  are  real  reservoirs  for  water  storage. 
It  is  a  marked  feature  of  the  plants  called  succulents.     In  the 
thick  stems  and  leaves  of  the  purslane  (Portulaca)  the  middle 
portion  is  largely  devoted  to  the  storage  of  water.     The  same  is 
true  in  the  thick  leaves  of  the  stonecrops  (Sedum).      In  some 
begonias  a  layer  of  cells  just  underneath  the  epidermis  of  the 
leaves  serves  as  a  water  reservoir.     Such  plants  when  growing 
under  moderate  climatic  conditions  have  little   need  of  water 
storage.     But  when  they  inhabit  alkaline  or  saline  soils,  or  soils 
in  dry  regions  as  they  sometimes  do,  this  habit  stands  them  in 
good  stead.     One  can  easily  demonstrate  their  power  of  retaining 
water  in  dry  weather  by  pulling  up  the  plants  and  leaving  them 
on  the  ground  or  by  hanging  them  on  the  fence.     They  remain 
fresh  for  a  long  time,  while  the  ordinary  plants  quickly  wilt. 
It  is  readily  seen  from  this  how  they  are  enabled  to  retain  life  in 
dry  situations  during  long  periods,  since  they  dole  out  the  water 
in  small  quantities.     The  most  remarkable  examples  of  the  power 
of  plants  to  retain  water  are  found  in  the  cacti,  where  immense 
trunks  with  no  leaves,  and  a  limited  surface  exposed  to  the  air 


49°  RELATION   TO  ENVIRONMENT. 

in  comparison  with  the  bulk  of  the  plant,  enable  the  plant  to 
resist  long  periods  of  excessive  drought.  In  fact  it  is  very  diffi- 
cult to  dry  out  the  stems  of  some  of  these  plants  provided  with 
water  storage. 

952.  Hydrophytic  structures. — From  what  we  know  of  the 
life  of  plants  on  the  dry  land  it  is  evident  that  water  plants  have 
some  very  different  problems  to  solve  in  their  life  processes. 
Some  of  these  adaptations  in  structure  are  as  follows: 

1.  Provision  for  attachment. 

2.  Provision  for  floating. 

3.  Provision  for  aeration. 

4.  Provision  for  distribution  of  food. 

5.  Provision  for  fruiting. 

6.  Provision  for  protection  from  water  movements. 

1.  Provision  for  attachment. — In  most  of  the  aquatic  flowering 
plants  and  ferns  attachment  to  the  ground  is  accomplished  as  in 
the  case  of  land  plants  by  roots.     The  roots  here  serve  chiefly  as 
holdfasts,  since  there  is  only  a  slight  development  of  root-hairs 
or  none  at  all  in  the  case  of  submerged  plants  anchored  in  the 
soil  or  rock  crevices.     Where  the  entire  plant  body  or  a  large 
part  of  it  is  immersed  in  water,  absorption  takes  place  through 
the  surfaces  in  touch  with  the  water.     The  development  of  vas- 
cular bundles  is  weak  or  wanting,  since  it  is  not  necessary  for  the 
plant  to  distribute  water  from  the  root  system.    See  note,  p.  712. 

2.  Provision  for  floating. — This  is  provided  for  by  large  inter- 
cellular spaces  which  contain  air  or  other  gases.     The  air-spaces 
in  some  stems  and  leaves  are  much  greater  than  the  bulk  of  the 
tissues  themselves,  and  serve  to  buoy  up  the  plant.     In  the  case 
of  many  plants  like   the  potamogetons,   where   the   leaves  are 
entirely  submerged,  or  some  of  them  float  on  the  surface  of  the 
water,   the   stems  are   slender  and  pliant,  and   do   not  possess 
strengthening  tissues  sufficient  for  support.     The  more  or  less 
upright  position  of  the  stems  is  due  to  the  floating  power  afforded 
by  the  numerous  large  air-spaces.      Oxygen  given  off  by  some 
filamentous  algae  in  the  process  of  photosynthesis  becomes  caught 
between  the  threads  in  a  tangle  and  floats  the  plant  on  the  sur- 


VEGETATION   TYPES.  49 ! 

face.  Some  of  the  blue-green  algas  develop  on  the  mud  in  the 
bottom  of  pools,  and  the  accumulation  of  gases  in  the  tangle  later 
buoys  them  up  to  the  surface  of  the  water. 

3.  Provision  jor  aeration. — Aeration  is  provided  for  through 
the  abundant  air-spaces  in  the  more  bulky  stems  and  leaves,  and 
also  by  the  ability  of  many  plants  to  float  to  the  surface  where 
the  threads  of  algae  are,  or  near  the  surface,  or  in  the  case  of 


Fig.  490. 

Swamp  forest  on  the  Gulf  Coast.  Bald  cypress  covered  with  hanging  moss 
(Tillandsia).  In  the  foreground  floating  plants,  the  water  hyacinth. 

floating  leaves  the  upper  surface  is  in  touch  with  the  air.  In 
the  latter  case  there  is  a  great  development  of  stomata  in  the 
upper  surface  of  the  leaf. 

4.  Provision  jor  distribution  oj  food. — The  epidermal  cells,  as 
well  as  the  tissues  of  most  water  plants,  are  provided  with  thin 
walls  where  they  are  in  contact  with  water.  This  permits  osmo- 
sis to  take  place  readily  between  the  surrounding  water,  which 
contains  dilute  food  solutions,  and  the  protoplasm  in  the  cells. 
Owing  to  the  loose  character  of  the  tissues  in  the  stems  and 
leaves,  diffusion  from  the  surface  throughout  the  tissues  is  not 
difficult. 


492  RELATION   TO  ENVIRONMENT. 

5.  Provision  for  fruiting. — For  most  of  the  aquatic  flowering 
plants  it  is  necessary  that  the  flowers  during  pollination  shall  be 
above  the  surface  of  the  water.     Some  curious  provisions  are 
made  for  this,  as  in  the  Vallisneria  spiralis.     The  slender,  grass- 
like  leaves  of  this  plant  are  submerged.     The  stem  which  bears 
the  pistillate  flowers  elongates  rapidly  at  time  of  flowering  and 
lifts  the  flower  to  the  surface.     At  the  same  time  the  staminate 
flower-buds,  which  are  borne  on  short  stems  at  the  bottom,  break 
off  and  float  to  the  surface,  where  they  open  and  the  pollen  is 
scattered.    After  pollination  the  flower-scape  coils  up  and  draws 
the  flower  underneath  the  water,  where  the  fruit  is  formed. 

6.  Protection  from  water  movement. — This  is  provided  for  in  a 
number  of  ways,  according  to  the  velocity  and  force  of  the  water, 
and  the  habit  of  the  plant.     The  pliant  condition  of  the  stems 
and  leaves  gives  them  considerable  mobility  in  the  water,  and 
they  are  protected  from  injury  which  wave  motion  or  currents 
would  inflict  on  a  more  rigid  habit.     Submerged  leaves  are  usu- 
ally small,  or  finely  dissected.     Many  of  the  marine  algae  are 
pliant  and  tough,  so  they  resist  the  violent  play  of  the  water,  or 
the  shock  of  the  breakers  against  the  rock.     Postelsia,  a  marine 
alga  along  rocky  shores  of  the  Pacific,  has  a  leathery  or  rubber- 
like  consistency.     There  is  an  upright  cylindrical  stem  2  to  3 
feet  high,  from  the  top  of  which  hang  strap-shaped  leaves.    These 
plants  with  others  of  similar  consistency  grow  near  the  edge  of 
the  water,  where  they  receive  the  full  force  of  the  breakers  as 
they  come  in  shore.    The  plants  are  laid  prostrate  with  each 
thrust  of  the  wave,  and  then  recover  as  it  recedes.     Certain 
fresh- water  algae,  as  species  of  Lemanea,  Cladophora,  etc.,  grow 
in  streams  where  the  water  plunges  over  rapids  or  falls.     Cer- 
tain species  grow  only  where  the  water  is  very  violent,  other 
species  of  the  same  genera  where  it  is  less  violent,  and  some 
species  of  Cladophora  as  well  grow  in  quiet  water. 

953.  Mesophytic  structures.  —  Those  plants  which  during 
the  growing  season  are  in  general  subject  to  medium  or  mod- 
erate conditions  of  environment  have  been  called  mesophytes. 
In  the  tropics,  where  the  heat  is  great  but  rains  abundant  and 


VEGETATION   TYPES.  493 

frequent,  the  vegetation  is  mesophytic  the  year  round.  In  tem- 
perate regions,  where  there  is  a  medium  rainfall  during  the  grow- 
ing season,  the  land  vegetation  is  mesophytic  during  this  season. 
But  during  the  winter  season,  or  during  the  dry  season  in  some 
regions  (part  of  California,  for  example),  the  conditions  of  en- 
vironment for  mesophytic  vegetation  are  extreme.  The  extreme 
cold  or  dryness  during  this  season  would  be  fatal  to  plants  with 
mesophytic  structures  were  it  not  for  the  fact  that  the  plant  is 
enabled  to  adapt  itself  to  the  periodical  change  in  environment 
by  discarding  the  mesophytic  habit  and  adopting  a  xerophytic 
one.  Mesophytes  of  temperate  regions  therefore  differ  from 
mesophytes  of  the  tropics,  and  have  been  termed  by  Schimper 
tropophytes,  because  they  turn,  as  it  were,  periodically  from 
one  condition  to  another. 

954.  Tropical   mesophytes.— Tropical    mesophytes  in  humid 
districts,  being  in  no  danger  from  extremes  of  dryness,  cold,  or 
excess  of  salts  in  the  substratum,  are  free  to  develop  to  the  high- 
est extent  foliage  structures,  without  interruption,   for  doing  a 
large  amount  of  work  in  transpiration,  respiration,  and  photosyn- 
thesis, which  are  necessary  for  rapid  growth.     We  have,  there- 
fore, the  luxuriance  and  permanence  of  foliage  in  humid  tropical 
regions.     The  foliage  leaf  reaches  its  highest  development.     To 
secure  the  highest  efficiency  in  work  we  have  already  learned 
that  the  leaf  is  broad  and  thin,  so  that  a  great  amount  of  surface 
in  proportion  to  the  bulk  is  exposed  to  light  and  air. 

955.  Temperate-region  mesophytes,  or  tropohytes.— Grow- 
ing season. — During  the  growing  season  the  general  character 
of  the  plant  structures  is  similar  to  that  of  the  humid  tropical 
region.     That  is,  the  conditions  are  such  as  to  favor  a  high 
development  of  foliage.      Where  the  soil  is  rich  and  there  is  an 
abundance  of  moisture  and  an  absence  of  drying  winds,  vegeta- 
tion in  temperate  regions  frequently  takes  on  a  tropical  aspect, 
even  in  the  northern  United  States  and  southern  Canada.     In 
drier  situations,  or  in  poorer  soil,  or  where  dry  winds  are  preva- 
lent, the  foliage  development  is  less  luxuriant.     In  fact  one  finds 
conditions  in  all  regions  so  varied  that  great  variations  in  the 


494  RELATION    TO   ENVIRONMENT. 

plant  population  show  how  sensitive  the  plant  habit  and  struc- 
ture are  to  environment.  So  in  temperate  regions  there  are  all 
gradations  from  vegetation  resembling  that  of  the  humid  tropics 
in  luxuriance  to  the  vegetation  of  arid  regions. 

956.  Resting  season. — During  the  winter  season,  or  in  some 
milder  climates  (California)  during  the  dry  summer  season,  the 
whole   aspect   of  the   mesophytic   vegetation  is   changed.     The 
forests  become  leafless,  except  in  some  for  the  sprinkling  of  the 
evergreen,  and  xerophytic  types  found  in  conifers,  heath  plants, 
etc.,   or  where   the  forest  is  dominated  by   these   types.     The 
deciduous  trees  and  shrubs  having  discarded  their  leaves,  which 
provided   them   with   an  immense   working   surface   during   the 
growing  season,  now  enter  upon  their  long  rest,  with  only  bulky 
structures  exposed  to  the  air,  the  surface  of  which  is  adapted  to 
greatly  resist  the  loss  of  water.     The  twigs,  branches,  and  trunks 
are  protected  by  their  bulk  and  by  the  covering  of  bark,  or  in 
some  cases  the  twigs  are  covered  also  with  hairs.     The  buds  are 
bulky,  and  while  there  are  small  and  delicate  leaves  and  tender 
growing  parts,  these  are  protected  from  loss  of  water  and  conse- 
quent death  from  drying  out  during  freezing  weather  by  the  cov- 
ering of  thick  dry  scales,  and  in  some  cases  by  the   additional 
protection  of  woolly  or  hairy  scales  underneath  these. 

957.  Provision  against  injury  and  loss  by  the  fall  of  the 
leaf. — Before  the  fall  of  the  leaf  much  of  the  nitrogenous  food  sub- 
stances in  the  leaf  slowly  passes  back  into  the  stem,  where  it  is 
stored  for  future  use.    While  this  is  going  on  in  deciduous  trees,  the 
petiole  of  the  leaf  near  its  point  of  attachment  to  the  stem  is  pre- 
paring to  cut  loose  from  the  latter  by  forming  what  is  called  a  sepa- 
rative layer  of  tissue.     At  this  point  the  cells  in  a  ring  around  the 
central  vascular  bundle  grow  rapidly,  so  as  to  unduly  strain  the 
central  tissue  and  epidermis,  making  them  brittle.     In  this  con- 
dition a  light  puff  of  wind  breaks  them  off,  and  the  separative 
layer  of  tissue  forms  a  covering  which  retards  loss  of  water  at  the 
wound. 

958.  Perennial  herbaceous  tropophytes. — With  the  approach 
of  winter,  perennial  herbaceous  tropophytes  prepare  for  exces- 


VEGETATION   TYPES.  495 

sive  cold  by  the  maturity  and  death  of  their  aerial  stems  and 
leaves.  The  underground  stems  and  the  roots  are  thus  pro- 
tected from  the  great  loss  of  water  which  would  result  should 
the  aerial  organs  retain  their  power  of  transpiration.  They  are 
further  protected  by  being  covered  by  soil,  humus,  leaves,  etc. 
In  such  plants  as  trillium,  Indian-turnip  (or  jack-in-the-pulpit), 
blood-root,  spring-beauty,  Solomon's-seal,  etc.,  the  underground 
stem  is  a  thick  rhizome  or  corm,  and  contains  an  abundance  of 
food  so  that  the  flowers  and  leaves  formed  in  late  summer  or 
early  spring  are  quickly  unfolded  and  appear  as  our  early  flowers. 
The  asters  and  goldenrods  do  not  have  such  an  amount  of  food 
stored  in  their  proportionately  smaller  underground  stems. 
Their  aerial  stem  and  leaves  require  a  longer  period  of  develop- 
ment, and  flowers  appear  from  midsummer  to  late  autumn. 
In  some  of  these  plants  sometimes  the  aerial  leaves  remain  green 
during  the  winter,  but  they  form  rosettes  near  the  ground,  and 
are  thus  protected  from  great  loss  of  water. 

959.  Annuals  and  biennials. — These,  as  suggested  in  para- 
graph 938,  may  be  considered  tropophytes,  since  annuals  every 
year  are  carried  through  the  period  when  the  environment  is 
austere  by  their  seed,   while  biennials  are  carried   through  in 
alternate  years  by  seed  and  by  the  rosette  type  of  leaf  arrange- 
ment close  to  the  ground,  and  by  the  short  subterranean  stem  of 
the  first  year. 

960.  Halophytic  structures. — Xerophytic  forms. — The  great 
body  of  partially  submerged  vegetation  of  the  salt-marsh  and 
other  shallow  saline  waters   is   furnished  with   xerophytic  habit 
and    structures.       The    roots    growing    in    soil    saturated    with 
highly  concentrated  salt  solutions  absorb  water  slowly,  and  con- 
sequently the  aerial  portions  of  the  stems,  as  well  as  the  leaves, 
must  be  able  to  retard  loss  of  water.     This  is  brought  about  by 
modifications  of  stems  and  leaves  similar  to  those  growing  in 
arid    regions.     These    modifications   are    reduced    leaf   surface, 
accompanied  often  by  a  thickening  of  the  leaf,  or  an  increase  in 
mass,  in  proportion  to  exposed  surface,  thickening  of  the  epider- 
mis, thickening  of  the  cuticle,  a  lessening  of  the  intercellular 


496 


RELATION   TO   ENVIRONMENT. 


spaces,  a  lesser  development  of  stomata,  hairy  covering,  deeply 
sunk  stomata,  slime-cells,  water  reservoirs,  etc.  These  plants 
are  sometimes  called  xerophytes,  but  they  differ  from  most  land 


Fig.  4900. 
Winter  condition  of  forest,  the  resting  season.     (Photograph  by  Rowlee.) 


xerophytes  in  their  power  to  absorb  water  with  a  higher  concen- 
tration of  salts  without  injury  to  the  protoplasm. 


CHAPTER  XLVIII. 

LAWS    AND    LIMITS    OF    PLANT    MIGRATION. 

961.  The  object  of  this  chapter  is  to  discuss  briefly  the  natural 
laws  of  the  movement  of  plants  over  the  earth,  not  only  the  move- 
ment of  plants  from  one  part  of  the  earth  to  another,  into  terri- 
tory beyond  its  "range,"  but  the  movement  of  plants  within  ter- 
ritory already  occupied  by  a  given  species.  Manifestly  when 
there  are  no  great  climatic  or  physiographic  changes  taking  place, 
the  laws  of  movement  in  general  would  be  the  same  whether  the 
species  was  moving  into  new  territory  or  moving  about  within 
territory  already  occupied  by  it.  The  word  distribution  is  some- 
times employed  instead  of  migration,  and  it  is  also  used  to  indi- 
cate the  "range"  or  the  territory  already  occupied  by  a  species, 
or  refers  in  general  to  the  location  of  the  different  elements  of  the 
earth's  floral  covering.  Migration  has  also  a  twofold  signifi- 
cance. It,  may  be  used  to  indicate  great  movements  of  plants 
from  one  region  to  another  during  prolonged  climatic  changes; 
or  movement  of  species  into  new  territory  where  conditions  are 
congenial  and  climate  is  stable,  or  back  and  forth  over  territory 
already  occupied.  The  terms  are  to  some  extent  interchange- 
able and  will  not  be  used  here  in  any  strict  sense,  since  the  con- 
nection in  the  text  will  usually  make  the  sense  clear.  It  is  not 
proposed  to  discuss  the  geographic  distribution  of  plants  in  the 
sense  of  the  "static"  distribution.  We  are  not  dealing  here  with 
the  floral  elements  of  the  earth,  but  with  the  vegetation  elements.* 

*  Flora,  or  floral  elements,  refers  to  species.  Vegetation  elements  refers 
to  the  character  of  the  vegetation  without  regard  to  species.  Thus  several 
different  species  or  floral  elements  may  show  but  one  vegetative  type. 

497 


RELATION   TO   ENVIRONMENT. 

The  distribution  of  various  vegetative  elements  is  treated  in  later 
chapters. 

I.   Relation  of  Plants  to  Earth's  Surface  as  a  Whole. 

962.  Northern   hemisphere. — In   considering  the  relation  of 
plants  to  the  earth's  surface  as  a  whole,  it  is  at  once  evident  that 
the    northern    hemisphere    possesses   a   much   larger   area    for 
plant  distribution  than  the    southern  hemisphere.      The  former 
comprises  the  great  continents  of  Europe,  Asia,  North  America, 
with  a  number  of  large  islands  in  the  West  Indies,  with  Green- 
land and  numerous  smaller  islands,  and  in  addition  the  northern 
parts  of  the  two  southern  continents,  South  America  and  Africa. 
The  distribution  of  plant  life  is  mainly  on  land,  and  for  a  limited 
distance  in  the  waters  along  the  ocean  and  lake  shores.      The 
great  part  of  the  oceans  and  of  the  larger  lakes  is  not  inhabited 
by  plants,  chiefly  because  of  the  depth  of  the  water  where  the 
plants  cannot  get  a  foothold,  and  because  of  oceanic  currents 
which  would  in  some  cases  carry  floating  plants  into  water  of  such 
extremes  of  temperature  that  they  could  not  exist.     In  some  of 
the  more  quiet  oceanic  waters,  as  in  the  Atlantic,  northeast  of  the 
West  Indies,  there  are  large  areas  of  floating  sargassum,  known  as 
the  Sargasso   Sea.  .    Areas  on  land,  devoid  of  vegetation,  are  the 
regions  of  perpetual  ice  and  snow,  as  in  alpine  heights  or  in  the 
farther  arctic  regions,  or  in  the  extreme  deserts.      The  greater 
habitable  land  area  of  the   northern   hemisphere,  together  with 
the  greater  extremes  of  climate  and  topography,  not  only  assures 
a  larger  number  of  individuals,   but  also   a  larger  number  of 
species    of    plants.     The    plant    population    is    therefore    more 
greatly  diversified  than  in  the  southern  hemisphere. 

963.  Southern  hemisphere. — This  includes  a  fraction  of  the 
habitable  land  area  of  the  globe,  the  larger  part  of  the  continents 
of  South  America  and  Africa,  the  large  island  of  Australia,  the 
East  Indies,  and  Madagascar,   with  numerous  smaller  islands. 
Besides  the  smaller  land  area,  the  climatic  and  land  variations 
are  not  so  great  as  in  the    northern   hemisphere.     The  actual 


PLANT  MIGRATION.  499 

land  area  of  the  southern  hemisphere  is  probably  greater  than 
appears  from  the  map,  since  it  is  believed  that  a  great  antarctic 
continent  underlies  the  ice  area  about  the  south  pole,  while  it  is 
believed  that  an  ice-covered  polar  sea  lies  at  the  north  pole. 

964.  Land  hemisphere,  or  continental  hemisphere.— The 
northern  and  southern  hemispheres  have  their  centres  at  the 
poles.  What  is  called  the  land,  or  continental,  hemisphere  is 
that  half  of  the  globe  which  contains  the  largest  possible  area  of 


Water  Hemisphere.  Land  Hemisphere. 

Fig.  491- 

Water  hemisphere  and  land  hemisphere  showing  proximity  of  continents  and 
islands  in  the  North  Polar  Zone. 

land,  and  has  its  centre  in  western  Europe.  It  includes  Europe, 
Asia,  Africa,  North  America,  the  northern  portion  of  South 
America,  and  the  entire  arctic  region.  It  is  interesting  to  note 
this  grouping  of  the  continents  over  one  half  of  the  earth,  as  it 
shows  how  near  the  areas  for  plant  distribution  are. 

965.  The  water  hemisphere,  or  oceanic  hemisphere. — This 
includes  the  southern  part  of  South  America,  Australia,  and  the 
East  Indies,  with  numerous  smaller  islands.  The  land  area  is 
small  and  the  variations  in  climate,  topography,  etc.,  which 
encourage  variation  and  increase  species  are  not  so  great  as  on 
the  continental  hemisphere.  The  migration  of  species  from  one 
island  to  another  is  not  so  easily  accomplished  because  of  the 
greater  distance,  though  the  distance  from  one  land  area  to  an- 
other is  not  more  than  about  one  hundred  miles  at  any  one  point. 


500  RELATION    TO   ENVIRONMENT. 

966.  Opportunities  for  migration  of  plants  between  conti- 
nents.— Continuity  of  land  areas  provides  opportunity  for  migra- 
tion of  plants.  Discontinuity  of  land  sets  up  a  barrier  to  plant 
migration.  Where  comparatively  large  land  areas  are  separated 
by  comparatively  narrow  bodies  of  water,  their  proximity  affords 
greater  possibility  of  the  plants  passing  the  barrier,  either  by 
floating  of  plant  parts,  or  seeds,  or  by  seeds  being  transported 
by  wind  or  animals.  Looking  at  the  map  of  the  northern  hemi- 
sphere in  the  region  of  the  arctic  circle,  it  is  seen  that  with  north 
British  America,  Alaska,  Siberia,  Russia,  Norway  and  Sweden, 
the  British  Isles,  Iceland,  Greenland,  there  is  a  nearly  continuous 
area  of  land  encircling  the  globe  just  below  the  pole.  Plant 
migration  from  one  continent  to  another  here  is  not  so  difficult  as 
farther  south.  Before  the  glacial  periods  it  was  much  warmer 
in  the  region  of  the  arctic  circle,  as  we  learn  from  the  fossil 
remains  of  tropical  plants  found  there.  In  that  remote  age 
(tertiary  times)  it  is  likely  there  was  communication  at  this  point 
between  plants  of  the  northern  continents.  But  it  is  very  differ- 
ent in  the  southern  hemisphere.  The  continents  of  Africa  and 
South  America  are  far  separated,  and  migration  of  plants  be- 
tween the  two  continents  is  well-nigh  impossible,  and  probably 
has  occurred  only  in  exceptional  cases.  These  relations  of  the 
continents  help  to  explain  why  it  is  that  there  are  so  many  resem- 
blances between  the  flora  on  the  continents  of  Europe,  Asia,  and 
North  America,  while  there  is  little  resemblance  between  the 
flora  on  the  continents  of  Africa  and  South  America. 


II.  Life  Regions,  Zones,  and  Areas. 

967.  Lines  of  plant  migration. — Plant  migration  takes  place 
along  lines  of  least  resistance.  Like  other  questions  in  plant 
distribution  this  one  is  complex.  In  general  it  may  be  said  that 
the  lines  of  least  resistance  are  those  of  like  temperature  areas, 
and  of  areas  with  like  moisture  content.  Plants  move  more 
freely  over  belts  the  temperature  and  moisture  conditions  of 
which  are  favorable  for  their  growth  and  reproduction.  Evi- 


PLANT  MIGRATION.  5OI 

dently  these  belts  vary  for  different  plants,  but  there  are  many 
plants  whose  temperature  requirements  are  the  same.  These 
come  into  competition  over  similar  areas.  The  temperature 
belts  favorable  for  the  growth  and  reproduction  of  plants  and 
animals  are  called  "life  zones."  In  general  "life  zones"  are 
transcontinental,  but  they  do  not  correspond  to  belts  limited  by 
lines  of  latitude  because  of  the  variations  in  altitude,  and  because 
of  warm  air-currents  from  bodies  of  water  which  affect  areas  that 
do  not  coincide  with  latitudinal  ones.  It  was  once  thought  that 
these  life  zones  coincided  with  isothermal  lines  or  belts,  i.e., 
those  lines  or  belts  formed  by  connecting  numerous  points  hav- 
ing the  same  mean  annual  or  seasonal  temperature.  While  this 
is  approximately  true  in  tropical  regions  where  the  fluctuations 
in  temperature  are  slight  throughout  the  year,  it  does  not  apply 
to  other  regions  because  of  the  great  fluctuations  of  tempera- 
ture, and  because  isotherms  show  the  mean  temperature  for 
arbitrary  periods  (year  or  month)  which  do  not  correspond  with 
the  period  of  growth  and  reproduction.  The  life  zones  are 
determined  by  the  physiological  constant  of  a  species,  and  may 
be  called  biothermal  lines,  or  biotherms. 

968.  Biothermal  lines,  or  biotherms. — The  physiological  con- 
stant of  a  species  is  determined  by  the  total  effective  heat — that 
is,  the  total  heat  above  6°  C.,  during  the  season  of  growth  and  re- 
production.    It  is  the  sum  of  the  mean  daily  temperatures  (above 
6°  C.)  during  the  season  from  the  time  when  growth  begins  in 
the  spring  (about  6°  C.  or  43°  Fahr.)  to  the  time   when  growth 
ceases  in  the  fall  (6°  C.  or  43°  Fahr.).     By  connecting  numerous 
points  having  the  same  total  heat  during  the  growing  season  the 
biothermal  lines  are  known.      These  lines,  which  in  general  are 
transcontinental,  mark  the  limits  beyond  which  species   do   not 
migrate  (except  in  rare  instances)  in  their  northward  distribution. 

969.  Life  regions. — Three  transcontinental   life   regions   are 
recognized  in  the  northern  hemisphere:   the  Boreal,  or  Northern; 
the  Austral,  or  Southern;  and  the  Tropical.     These  regions  were 
first  established  by  Alexander  von  Humboldt  when  he  divided 
the  globe  into  the  great  life  belts.     The  regions  were  separated 


502 


RELATION   TO   ENVIRONMENT. 


PLANT  MIGRATION.  5O3 

along  isothermal  lines,  since  heat  was  then  recognized  as  the 
greatest  factor  in  the  distribution  of  plants  and  animals.  But 
since  the  mean  temperature  of  arbitrary  periods  (annual  or 
monthly)  does  not  coincide  with  the  mean  temperature  of  the 
season  for  growth  and  reproduction,  lines  were  established  by 
Merriam  which  coincide  with  the  physiological  constant  of  the 
species.  These  lines  form  more  accurate  limits  of  the  life 
regions,  and  may  be  called  biothermal  lines,  or  biotherms. 

The  Boreal  region  covers  the  whole  of  the  northern  part  of 
the  continent,  from  the  polar  sea  southward  to  near  the  northern 
boundary  of  the  United  States,  and  farther  south  occupies  a  nar- 
row strip  along  the  Pacific  coast  and  the  higher  parts  of  the 
three  great  mountain  systems,  the  Sierra  Cascade  Range,  the 
Rocky  Mountains,  and  the  Alleghanies. 

The  Austral  region  covers  the  whole  of  the  United  States  and 
Mexico,  except  the  boreal  mountain  heights  and  the  tropical 
lowlands. 

The  Tropical  region  covers  the  southern  part  of  the  peninsula 
of  Florida,  the  greater  part  of  Central  America,  the  lowlands  of 
southern  Mexico  south  of  the  table-land,  and  a  narrow  strip  on 
each  side  of  Mexico,  which  follows  the  coast  northward  into  the 
United  States. 

970.  Life  zones  and  areas.— The  flora  and  fauna  within  each 
of  these  great  regions  are  not  homogeneous,  but  present  marked 
differences,  which  have  led  to  the  subdivision  of  each  region  into 
a  number  of  minor  belts  or  areas,  characterized  by  particular 
associations  of  animals  and  plants.  Thus  the  Boreal  region  is 
divided  into  three  transcontinental  belts  or  zones,  known  re- 
spectively as  the  Arctic,  Hudsonian,  and  Canadian;  the  Austral 
region,  into  three  transcontinental  belts,  known  as  the  Transi- 
tion, Upper  Austral,  and  Lower  Austral.  The  Tropical  region 
is  likewise  divisible,  but  the  tropical  areas  within  the  United 
States  are  of  small  extent.  These  transcontinental  zones  are 
further  divided  into  eastern,  central,  and  western  areas,  because 
of  the  influence  and  distribution  of  rainfall.  The  following 
table  will  show  the  subdivisions: 


504 


RELATION   TO   ENVIRONMENT. 


Boreal  Region.  . 


Lines  of  stress  due  to  heat. 

Arctic  or  Arctic- 
Alpine  Zone. 
Hudsonian  Zone. 
Canadian  Zone. 

Transition  Zone 


Lines  of  stress  due  to 
rainfall  or  drought. 


Austral  Region. 


Upper  Austral  Zone. 


Lower  Austral  Zone. 


Tropical  Region. 


(  Alleghanian  Area, 
i  Arid  Transition  Area. 
Pacific    Coast   Transi- 
\      tion  Area. 

;  Carolinian  Area. 

1  Upper  Sonoran  Area. 

f  Austroriparian  Area. 
\  Lower  Sonoran  Area. 

Humid  Tropical 
Arid  Tropical. 

971.  The  great  lines  of  stress. — There  are  here  shown  two 
great  systems  of  parallel  lines  of  stress  which  influence  and  limit 
plant  migration.     One  of  these  systems  of  stress  is  traceable  to 
the  factor  heat,  and  the  stress  lines  are  in  general  transconti- 
nental (east  and  west).     In  the  eastern  and  western  portions  of 
the  continent,  however,  these  temperature  stress  lines  are  de- 
flected far  to  the  south  because  of  the  mountain  ranges  and 
become    parallel    with    continental    lines.     So    mountain    ranges 
constitute  lines  of  stress,  but  the  great  factor  influencing  plants 
is  heat,    since   plants  in   attempting   to   cross   mountain   chains 
meet  with  the  extreme  cold  of  mountain-tops.     The  other  sys- 
tem of  stress  lines  is  due  to  difference  in  rainfall;  the  interior  of 
the  continent  having  a  slight  amount  of  rainfall  as  compared 
with  the  abundant  rainfall  nearer  the  coast  and  along  the  moun 
tain  ranges  (except  in  the  southwest),  these  lines  run  across  the 
temperature  stress  lines.     Large  bodies  of  water  also  constitute 
lines  of  stress. 

972.  Lesser  lines  of  stress.— Lesser  lines  of  stress  are  formed 
by  streams  and  small  bodies  of  water,  as  well  as  by  the  lesser 
physiographic  variations  of  the  earth's  surface.     For  example, 
between   ponds,    marshes,    swamps,    etc.,    and   the   surrounding 
higher  elevations;    between  rocky  areas,  sandy  areas,  and  soil 


PLANT  MIGRATION.  50$ 

rich  in  humus;  between  alkaline  areas  and  those  with  a  small 
salt  content,  and  so  on.  A  study  of  the  vegetation  elements 
along  these  lesser  lines  of  stress  is  possible  in  any  locality  where 
one  may  see  the  struggle  along  the  border  line  between  plants 
occupying  different  kinds  of  territory. 

973.  Total  heat  as  limiting  factor  in  north  and  south  migra- 
tion.— According  to  Merriam  plants  and  animals  are  limited  in 
their  northward  distribution  by  the  sum  total  of  heat  (above 
6°  C.)  during  the  period  of  growth  and  reproduction  (the  sum 
of  the  effective  temperatures),  but  they  are  limited  in  their  south- 
ward distribution  by  the  mean  temperature  of  the  hottest  part 
of  the  year.     Since  some  plants  and  animals  require  a  larger 
sum  total  of  heat  than  others,  they  are  drawn  into  these  different 
life  zones  in  accordance  with  their  temperature  requirements. 
But  singularly  on  the  Pacific  slope  there  is  greater  mixing  of 
boreal  and  austral  forms,  the  boreal  forms  extending  far  south- 
ward and  the  austral  forms  far  northward.     This  is  due  to  the 
more  equable  temperature  during  the  reproductive  period.      The 
comparatively  low  mean  temperature  during  the  summer  per- 
mits northern  forms  to  go  far  southward;    while  the  high  sum 
total  of  effective  heat  permits  southern  forms  to  go  far  north- 
ward (see  characters  of  the  Pacific  coast  transition  area,  Chap- 
ter LVII). 

974.  Limiting  factor  for  east  and  west  distribution  in  United 
States. — On  the  other  hand,  plants  and  animals  are  limited  in 
their  east  and  west  distribution  in  the  austral  and  tropical  regions 
of  North  America  by  difference  in  rainfall  and  humidity,   the 
great  arid  area  in  the  centre  of  the  continent  affording  an  effec- 
iu;il  barrier  to  the  west  or  east  movement  of  the  east  or  west 
forms,  while  the  forms  of  the  arid  area  are  prevented  from  mov- 
ing east  or  west  of  this  area  partly  by  the  dominance  of  the  forms 
in  the  humid  area  and  partly  by  the  specialized  character  of  arid 
area  plants  unfitting  them  for  humid  climates.     The  mountain 
ranges  also  to  some  extent  limit  east  to  west  distribution,  but 
the  factor  here  is  heat,  and  these  areas  as  pointed  out  above  are 
southward  extensions  of  the  general  transcontinental  zones. 


506  RELATION   TO   ENVIRONMENT. 

These  zones  and  areas  established  by  Merriam,  and  the  laws 
governing  them,  have  not  yet  been  subjected  to  a  sufficiently 
thorough  test  so  far  as  plants  are  concerned,  and  there  are  many 
cases  of  plant  distribution  which  they  do  not  adequately  explain. 
Nevertheless  they  are  in  general  accord  with  several  great  fac- 
tors of  plant  distribution  and  are  worthy  of  careful  study  and 
test.  Modifications  it  may  be  necessary  to  make,  though  in  gen- 
eral the  fundamental  principles  seem  well  grounded.  The 
limits  of  these  life  zones  and  areas  in  the  United  States  can  be 
seen  by  consulting  Fig.  492.  The  limits  and  the  characteris- 
tics of  the  life  zones  and  areas  of  North  America  are  given  in 
Chapter  LVII. 

III.  Methods  and  Causes  of  Plant  Migration. 

975.  Advantages  of  plant  migration. — The  advantages  accru- 
ing to  plants  through  their  power  or  tendency  to  migrate  is  that 
individuals  of  a  species  are  increased  by  extending  their  area  of 
occupation.     Whether  the  plant  concerned  occupies  any  given 
area  to  the  exclusion  of  other  species  or  not,  an  extension  of  the 
area  provides  for  an  increase  in  individuals,  and  the  perpetua- 
tion of  species  is  thus  more  surely  safeguarded.     It  increases  the 
factor  of  safety  for  existence:     ist.  By  the  larger  number  of 
individuals  possible  over  a  larger  area.     2d.  The  safety  of  some 
is  assured  in  case  of  disaster  to  others  in  a  certain  region.     Disas- 
ter may  come  by  sharp  competition  of  other  species,  or  by  the 
destructive  effect  of  physical  changes  in  the  topography  of  cer- 
tain areas.     For  example,  in  time  of  flood,  areas  being  covered 
by  sand,  gravel,  or  other  rock  debris;   or  by  changes  in  the  cli- 
mate, etc.     3d.  The  species  often  gains  in  vigor  by  coming  under 
new  conditions,  better  soil  conditions,  more  favorable  climatic 
conditions,  etc. 

976.  Structural  characters  favoring  plant  migration. — Many 
of  these  characters   are  discussed  more  fully  in  the  chapter  on 
"Seed  Dispersal,"  and  others  in  the  chapter  on  "Stems,"  etc. 
The  mere  enumeration  of  some  of  these  characters  is  given  here. 


PLANT  MIGRATION. 

1.  Seeds. — ist.  The  buoyancy  of  seeds  produced  by  the  devel- 
opment of  so-called  "wings"  on  the  elm,  maple,  etc.,  the  pappus 
of  the  composites,  and  other  hairy  or  woolly  outgrowths,  form 
part  of  the  seed  or  fruit  which  enable  it  to  catch  the  wind.     Small 
size  and  lightness  of  many  seeds  also  give  them  a  certain  amount 
of  buoyancy.     2d.  The  development  of  structures  for  grasping 
hold  upon  other  objects;    for  example,   barbs    and    hooks  on 
seeds  or  fruits  for  clinging  to  animals.     3d.  The  use  of  seeds  as 
food  by  animals.     4th.  Seeds  which  are  capable  of  floating  on 
the  water. 

2.  Fruit. — There  are  many  fruits  which  are  used  for  food  by 
animals  and  the  seeds  of  which  often  pass  through  the  body 
uninjured,   and  thus  often  gain  wide  distribution.     Exploding 
fruits  also  bring  about  the  dispersal  of  seed,  as  in  the  vetches, 
the  touch-me-not,  the  fruit  of  the  witch-hazel,  or  of  spores,  as  in 
the  sporangia  of  ferns,  or  of  some  of  the  fungi. 

3.  Tumble-weeds. — Several  kinds  of  tumble-weeds  are  known, 
some  of  which  are  popularly  spoken  of  as  "resurrection-plants," 
especially  certain  species  of  club-mosses  (Lycopodium).      These, 
as  is  well  known,  in  dry  weather  curl  their  stems  into  a  more  or 
less  round,  compact   ball,  and  in  so  doing  the  roots  are  fre- 
quently torn  from  their  attachment  to  the  soil,  and  the  ball  is 
rolled  along  by  the  wind  over  plains  to  considerable    distances. 
During  the  rainy  season  these  plants,  which  have  retained  their 
life  in  the  dry  condition,  expand  and  the  roots  take  hold  of  the 
soil  again.     Parts  of  plants,  as  the  seed-bearing  portion  of  certain 
grasses,  are  often  broken  during  heavy  winds,  and  are  blown  or 
rolled  for  a  considerable  distance  over  the  ground,  thus  providing 
for  the  distribution  of  seed. 

4.  Floating  of  broken  branches. — In  the  case  of  certain  trees 
or  shrubs  growing  next  to  water  the  branches  are  often  broken 
by  the  wind  and,  floating  to  new  places,  sometimes  aid  in  the 
distribution  of  the  species. 

5.  Prostrate  creeping   plants  or  plants  with  a  more  rampant 
habit  migrate  through  a  system  of  natural  layering.     In  pros- 
trate or  creeping  plants,  like  the  strawberry,  or  trailing  roses,  the 


5o8 


RELATION   TO  ENVIRONMENT. 


Fig.  493- 
Walking-fern,  climbing  down  a  hillside. 


PLANT  MIGRATION.  509 

stems  take  root  he*-e  and  there,  and  thus  slowly  but  surely  extend 
the  area  of  occupation  by  the  species.  Plants  of  more  rampant 
habit,  like  the  blackberries,  or  certain  other  roses,  take  root  at 
the  tips  of  their  branches,  where  they  come  in  contact  with  the 
ground,  and  new  shoots  develop  at  this  point.  This  habit  is 
sometimes  spoken  of  as  the  "walking"  habit,  and  is  well  illus- 
trated by  the  "walking-fern"  (Fig.  493). 

6.  Underground  creeping  stems  or  roots. — Of  this  type  there  are 
a  large  number  of  well-known  examples,  the  underground  shoots 
of  many  grasses  for  example,  of  ferns  like  the  sensitive  fern,  or 
bracken-fern.  Among  those  which  extend  their  distribution 
through  roots,  a  striking  example  is  that  of  certain  species  of 
sumac.  In  New  York  State  several  species  of  sumac  by  their 
seeds  gain  foothold  in  abandoned  fields  or  in  pastures.  The 
roots  of  these  species  spread  many  feet  just  underneath  the  sur- 
face of  the  soil,  and  each  year  from  these  roots  new  shoots  are 
developed.  The  sumac  often  spreads  from  5  to  10  feet  per  year 
in  this  way. 

977.  Causes  of  plant  migration. — In  general  the  causes  of 
plant  migration  may  be  grouped  under  two  kinds  of  factors: 
i  st.  What  may  be  known  as  biotic  factors.  2d.  Physical  and 
climatic  factors. 

1.  Biotic  factors. — These  factors  are  found  both  in  the  agency 
of  animals  ,and  plants  themselves.     Animals  bring  about  plant 
migration  through  the  eating  of  fruits  and  seeds,  or  by  dispersal 
of  seeds  which  cling  to  their  bodies.     Causes  of  plant  migration 
initiated  by  plants  themselves  are  found  in:    ist.  Fertility  of 
species  by  which  seed  results.     Plants  which  have  the  power  to 
deve'op  large  numbers  of  fertile  seeds  with  the  best  means  for 
seed  distribution  not  only  gain  distribution  through   the  seed, 
but  by  the  crowding  of  certain  areas  bring  about  pressures. 
2d.  The   centrifugal  habit  of  self-propagation   by  runners,   by 
layerings,  or  by  the  propagation  of  stems  from  separate  roots. 
3d.  The  factor  of  adaptation  to  environment,  or  acclimatization. 

2.  Physical  and  climatic  factors. — Some  of  these  have  already 
been  mentioned  under  the  head  of  structural  characters  favor- 


510  RELATION    TO   ENVIRONMENT. 

ing  plant  migration,  ist.  There  are  certain  physical  factors,  as 
wind,  water,  which  float  seeds  of  various  plants  to  great  dis- 
tances. Then  the  increase  of  depth  of  water  or  the  lowering  of 
depth  of  bodies  of  water  forces  to  a  limited  extent  migration  of 
plants  along  other  shores.  2d.  Tensions  in  fruits;  for  example, 
exploding  fruits.  3d.  Climatic  pressures.  These  pressures  are 
brought  about  from  variations  in  the  climate,  those  variations 
which  extend  over  long  periods  of  time.  The  most  noted  of 
these  pressures  upon  plant  distribution  occurred  in  what  is 
known  as  glacial  times.  During  this  epoch  of  the  earth's  his- 
tory a  great  ice-sheet  formed  in  Canada  and  British  America, 
flowed  down  across  the  border  and  over  a  great  portion  of  the 
northern  United  States.  This  great  change  in  the  climate,  the  in- 
tense cold  for  so  many  ages  gradually  extending  southward,  forced 
the  plants  of  northern  North  America  southward.  Those  which 
were  not  able  to  migrate  in  advance  of  the  glacier  perished. 

978.  Action  of  glaciers. — Geologists  have  learned  from  a  study  of  the 
formation  and  movement  of  mountain  glaciers  and  of  the  great  ice -sheets 
covering  Greenland  and  other  arctic  lands  how  to  determine  the  former 
presence  of  similar  glaciers  by  marks  which  they  have  left  upon  the  sur- 
face of  the  land.     These  great  masses  of  ice,  possessing  enormous  weight, 
grind  upon  the  rock  surface,  ploughing  out  basins  and  scouring  the  rocks 
over  which  they  pass.     The  great  scouring  action  is  produced  by  rocks 
which  become  fastened  in  the  lower  surface  of  the  glacier,  and  so  shoved 
along  by  its  movement,  ploughing  and  gouging  into  the  solid  rock  below. 
Along  the  advancing  edge  of  the  glacier  or  ice-sheet,  where  it  is  melting, 
these  r6cks,   gravels,   and  clays,   mixed  together,   are   deposited,   forming 
what  are  known  as  the  terminal  moraines. 

979.  Limits   of  the   great   glaciers. — According  to  geologists,  the  great 
ice-sheet  which  flowed  down  over  the  northern  United  States  was  gathered 
on  the  uplands  of  Canada  and  British  America  by  a  great  and  long-con- 
tinued fall  of  snow.     The  pressure  of  great  bodies  of  snow  formed  wijh 
the  ice-sheet,  and  this,  by  its  own  weight,  was  forced  to  flow  to  the  south- 
ward where  there  was  less  snow  on  account  of  the  warmer  temperature. 
The   ice-sheet  in  its  southern  movement  extended  down  to   the  "southern 
border   of  New   England,    across   New   Jersey,    Pennsylvania,  and   south- 
western New  York,  and  then  followed  a  crooked  course  north  of  the  Ohio 
River.     It  nearly  followed  the  Missouri  River  across  Missouri,  and  then 
northwest  through  Nebraska  and  the  Dakotas  and  Montana,     Mu^H  of 


PLANT  MIGRATION.  51 1 

our  western  mountain  region  where  a  few  remnant  glaciers  are  found  was 
covered  with  ice,  continuing  into  the  great  ice-fields  of  British  Columbia." 
The  ice  flowed  over  the  north  Alleghany  Mountains,  over  the  Adirondacks 
in  New  York,  smoothing  and  rounding  them.  All  along  the  southern 
line  of  the  glacier  are  the  waste  materials,  forming  terminal  moraines, 
which  have  been  carefully  studied  by  geologists.  Evidence  goes  to  show 
that  after  the  first  onward  movement  of  the  ice -sheet  a  warmer  period 
came,  and  the  ice-sheet  retreated  northward,  and  many  ages  afterward 
extended  again  to  the  south,  nearly  to  its  former  limit.  Since  this  last 
glacial  period  the  ice  has  receded  until  the  glaciers  now  occupy  only  the 
higher  mountains  in  the  northern  Rockies,  and  Alaska  and  Greenland. 

During  the  same  period  a  similar  ice -sheet  covered  all  northern  Europe, 
extending  as  far  south  as  the  Thames  Valley  in  the  British  Islands;  the 
North  and  Baltic  Sea  basins5  northern  Germany,  and  northern  Russia 
were  occupied. 

980.  Effect  of  the  cold  wave  on  plant  migration. — The  pres- 
ence and  movement  of  these  great  sheets  of  ice  southward  over 
the  northern  hemisphere  forced  the  migration  of  northern  species 
southward.      As  the  ice-sheet  reached  into  the  temperate  regions 
it  forced  in  advance  of  it  the  species  from  the  temperate  regions 
southward.     As    the    glacier    retreated    northward,    the    plants 
which  were  able  to  survive  by  southward  migration  again  mi- 
grated northward.     Geological  evidence  goes  to  show  that  there 
were  a  number  of  movements  back  and  forth  of  the  ice-sheet. 
This    great    climatic    pressure,    therefore,    fluctuated     for    long 
periods,  forcing  the  plants  southward,  then  again  yielding  and 
allowing  the  plants  to  take  up  their  former  positions,  when  again 
they  would  be  forced  southward,  and  so  on. 

981.  Evidences  of  plant  migration  in  glacial  times. — In  stud, 
ies  of  the  distribution  of  the  plants  of  North  America  and  Europe 
and  Asia,  there  are  at  present  evidences  of  this  migration  of 
plants  southward.      Many  arctic  plants  which  at  that  time  moved 
southward  are  now  left  on  the  higher  mountain  peaks,  or  in  the 
cool    sphagnum   moors   formed   among   some   of   the   terminal 
moraines.     With  the  proximity  of  the  continents  in  the  arctic 
circle  there  is  reason  to  believe  that  in  former  times  plants  mi- 
grated readily  between  the  continents  of  North  America,  Europe, 
and  Asia.     During  glacial  times  these  were  forced  southward, 


512  RELATION   TO   ENVIRONMENT. 

both  in  Europe,  North  America,  and  Japan.  Evidence  of  this 
is  shown  in  the  close  relationship  of  the  flora  of  northern 
Europe,  North  America,  and  Japan.  Many  species  and  genera 
of  plants  are  found  in  these  countries  which  are  the  same.  Under 
the  present  conditions  of  the  climatology  of  the  earth,  it  would 
be  impossible  for  the  plants  to  communicate  to  such  an  extent 
as  to  explain  the  presence  in  these  different  continents  of  such  a 
large  number  of  the  same  species.  While  in  the  seed  plants 
there  are  many  similarities  in  the  flora,  and  many  species  and 
genera  are  identical;  in  the  lower  forms,  among  the  algae,  fungi, 
liverworts,  and  mosses,  there  is  an  even  greater  similarity.  This 
leads  us  to  believe  that  even  microscopic  plants  like  the  fungi 
and  algae  migrated  under  these  conditions  along  with  the  seed 
plants.  The  parasitic  fungi  moved  along  with  their  hosts,  and 
saprophytic  fungi,  like  the  mushrooms,  followed  the  movements 
of  forest  trees,  growing  on  dying  or  dead  trunks,  upon  the  leaves, 
and  leaf -mold  in  the  forest.  The  aquatic  fungi  and  the  fresh-water 
algae  likewise  moved  southward  with  the  aquatic  flowering  plants. 
The  fact  that  so  many  of  the  fresh-water  forms  of  the  fungi  and 
a'gae  are  identical  with  many  of  those  in  northern  Europe  sug- 
gests that  in  former  times  the  continents  in  the  arctic  circle  were 
very  near  together,  if  not  actually  connected,  that  the  climate 
was  milder,'  and  that  there  was  a  migration  of  these  fresh-water 
plants  between  the  continents  This  might  be  brought  about 
by  a  possible  continuity  of  land  and  fresh-water  areas,  or  through 
the  migration  of  water-fowl  tne  spores  of  algae  and  fungi  cling- 
ing to  their  feet  could  be  transported  across  land  areas  or  chan- 
nels of  salt  water,  when  these  were  not  too  wide,  and  lodged  in  the 
fresh-water  pools,  or  lakes,  or  streams  of  another  near-by  conti- 
nent. 

982.  Present  climatic  pressures. — Other  climatic  pressures 
also  existed  and  continue  to  the  present  time.  In  the  humid 
tropics  large  numbers  of  individuals  of  different  species  were 
propagated,  which  produced  a  pressure  northward  and  south- 
ward from  this  point,  but  those  moving  southward  on  the  north- 
ern hemisphere  come  in  contact  with  those  moving  northward, 


PLANT  MIGRATION.  $13 

and  here  a  lateral  pressure  is  exerted  which  crowds  the  plants 
to  the  west  and  east.  Pressures  also  exist  in  the  borders  of  arid 
regions.  The  fertility  of  aggressive  species  wherever  they  occur 
tends  to  produce  pressures  in  all  directions. 

983.  Barriers  to  plant  migration. — There  are  a  number  of 
barriers  which  plants  meet  in  their  migration  over  the  surface  of 
the  earth.  In  general  terms  we  might  speak  of  four  when  look- 
ing at  the  world  as  a  whole,  ist.  Kinds  of  climate:  regions  of 
great  heat  or  cold,  of  dryness  or  moisture,  etc.  All  these  regions 
oppose  obstacles  to  the  entrance  and  passage  of  plants  which 
are  accustomed  to  live  in  different  climates.  2d.  Kinds  oj  soil; 
for  example,  the  alkaline  deserts  and  the  great  salt  steppes  pre- 
sent effectual  barriers  to  the  passage  of  plants  not  provided  with 
adaptations  which  would  enable  them  to  live  under  such  ex- 
treme conditions  3d.  Discontinuity  oj  land.  Here  bodies  of 
water  present  a  barrier  to  the  passage  of  plants  from  one  conti- 
nent to  another,  or  from  one  island  to  another,  which  are 
separated  by  broad  lakes  or  seas.  A  good  illustration  of  this  is 
shown  in  the  relation  of  the  continents  of  the  southern  hemi- 
sphere as  compared  with  those  of  the  northern  hemisphere 
already  pointed  out.  4th.  Mountain  chains.  High  mountain 
chains,  because  of  the  great  cold,  often  form  impassable  barriers 
for  plants;  good  illustrations  of  this  are  shown  in  a  comparison 
of  the  number  of  species  of  plants  in  Europe  and  North  America 
and  their  distribution.  Under  the  high  climatic  pressures  which 
existed,  for  example,  in  glacial  times,  the  plants  of  North  Amer- 
ica met  with  no  barrier  in  their  southward  movement;  prob- 
ably a  large  percentage  of  them  survived.  In  North  America 
the  mountain  chains  were  parallel  with  the  migratory  movement 
and  permitted  the  southward  flow  and  return  of  the  species. 
On  the  contrary  on  the  continent  of  Europe  dur'ng  the  same 
period  in  their  southward  movement  the  plants  met  with  an 
impassable  barrier  in  the  Alps  and  Pyrenees  Mountains,  which 
extend  east  and  west  across  southern  Europe.  Many  of  the 
species  thus  perished  and  were  not  left  to  join  in  the  return  move- 
ment in  populating  the  continent  after  the  disappearance  of 


5 14  RELATION    TO  ENVIRONMENT. 

the  ice-sheet.  Likewise  the  Alps  and  Pyrenees  presented  a 
barrier  to  the  northern  movement  of  the  plants  of  southern 
Europe.  The  Rocky  Mountains  afford  a  barrier  between  the 
flora  of  the  Pacific  coast  and  the  country  to  the  east. 

983a.  Conflict  of  species  in  migration. — This  is  one  of  the 
most  noticeable  features  in  plant  migration.  With  the  means  for 
movement  with  which  plants  are  provided,  together  with  the 
pressures  exerted,  forcing  them  to  move,  they  are  constantly 
reaching  out  for  new  territory  and  struggling  to  hold  that  which 
they  already  occupy.  The  competition  becomes  severe  be- 
cause of  the  large  number  of  species  which  are  adapted  to  live 
under  similar  conditions.  Some  have  compared  the  struggles 
of  plants  to  occupy  new  territory,  or  to  maintain  their  hold  upon 
their  own,  to  the  competition  which  exists  among  human  soci- 
eties. Every  plant  must  be  able  to  propagate  itself  and  to  hold 
territory  in  competition  not  only  with  climatic  conditions,  but 
also  with  other  plants  entering  the  same  region.  It  must  either 
hold  its  territory  or  cede  it  to  its  more  successful  rivals.  Thus 
plants  which  are  best  adapted  to  live  under  the  conditions  of  a 
given  territory  are  those  which  survive,  while  the  weaker  ones 
are  driven  out,  or  exterminated,  or  occupy  a  very  subordinate 
place  in  the  society. 


CHAPTER  XLIX. 

PLANT    FORMATIONS. 

984.  The  general  formations. — Wherever  the  conditions  of  en- 
vironment  are   such   as   to  develop   one   or   another  vegetation 
type  in  such  abundance  that  it  becomes  the  dominating  vegeta- 
tion type  of  the  region  or  area  it  is  known  as  a  formation.     A 
single  plant  or  a  few  plants  may  represent  a  vegetation  type, 
but  do  not  constitute  a  formation.     The  massing  together  of 
a  vegetation  type,  though  it  may  be  represented  by  many  widely 
different  species,  so  that  the  area  is  characterized  by  this  type 
as  the  dominant  one,  constitutes  a  formation.     There  may  be 
other   types   mixed   which   either   appear   at   certain   favorable 
seasons  (example,  the    rainy-season  flora  in  the  desert  forma- 
tions)  or  represent  a   few   subordinate  individuals.     The  total 
combined  dominant   vegetation  of  any  one  type   constitutes  a 
general   formation.     The   general   formations   may  be  grouped 
first  in  four  divisions. 

1.  Climatic  Formations. 

2.  Edaphic  Formations. 

3.  Aquatic  Formations. 

4.  Culture  Formations. 

I.  Climatic  Formations. 

985.  The  plant  covering  of  the  earth  is  not  uniform. — This  is 
due  in  a  great  measure  to  the  lack  of  uniformity  in  climate, 
topography,    and    soil.     Climatic   influences    extend   over   wid^ 


5l6  RELATION   TO   ENVIRONMENT. 

regions.  They  do  not  govern  special  types  of  plant  communities. 
Climate  controls  the  general  type  of  vegetation  of  a  region.  In 
the  sense  of  control  there  are  two  climatic  factors,  temperature 
and  moisture,  especially  soil  moisture.  Temperature  exerts  a 
controlling  influence  only  over  the  general  vegetation  type  where 
the  total  heat  during  the  period  of  growth  and  reproduction 
is  very  low.  This  occurs  in  polar  lands,  so  that  the  arctic  zone 
(including  alpine  areas  on  high  mountains)  has  a  distinct  gen- 
eral vegetation  type  which  is  controlled  by  temperature.  This 
is  the  arctic  vegetation  of  the  Cold  Wastes,  or  Tundra,  the  land 
where  the  ground  in  many  places  is  perpetually  frozen  and 
only  thaws  out  on  the  surface  during  the  short  summer  period. 
In  the  temperate  and  tropical  regions  of  the  globe,  moisture, 
not  heat,  is  the  controlling  factor  in  determining  the  general 
vegetation  types.  These  are  in  general  coincident  with  rain- 
fall distribution,  and  there  are  here,  according  to  Schimper,  three 
great  vegetation  types  controlled  by  climate:  the  woodland, 
the  grassland,  and  the  desert.  There  are,  then,  according  to 
Schimper,  four  climatic  formations,  as  follows: 

986.  (i.)  The  Arctic- Alpine    Formation.— The    determining 
climatic  cause  is  temperature,  as  indicated  above. 

987.  (2.)  The  Woodland  Formation.— This  is  characterized 
by  woody  plants,  whether  trees  or  shrubs.     If  a  close  formation 
of  trees,  it  is  a  forest;   if  clumps  of  shrubs  separate  the  trees  so 
the  crowns  do  not  meet,  it  is  a  "bush";  or  if  the  shrubs  dominate, 
it  is  a  thicket.     The  woodland  formation  is  a  close  formation, 
i.e.,  the  climatic  conditions  are  such  that  freedom  of  growth  is 
permitted  over  the  entire  area.     The  plants  are  not  struggling 
against  climate,  but  compete  with  each  other,  and  the  entire 
ground   being   occupied    the    formation   is   close.     If    there   are 
bare  plates  here  and  there,  or  places  occupied  by  herbage,  they 
are   mere   accidents,   due   to   factors  acting   temporarily,   or  to 
differences   of   soil    (i.e.,    ground).     There   also   may   be   spots 
which  are  xerophytic  or  spots  which  are  hydrophytic,  but  these 
are  due  to  soil,  not  climatic  factors.     The  unfavorable  condi- 
tion of  the  soil  here  overcomes  for  the  time  the  climatic  influence. 


PL  A  N  T  FORMA  TIONS.  5  I  / 

The  .entire  region  is  a  potential  woodland  formation,  i.e.,  if  left 
to  the  operation  of  natural  forces,  in  time  a  forest  would  develop 
over  the  entire  area  unless  interrupted  by  great  climatic  or 
physiographic  changes.  It  is  the  region  of  normal  to  excessive 
rainfall,  and  in  North  America  covers  practically  the  Hud- 
sonian  and  Canadian  zones  and  the  Alleghanian,  Carolinian, 
Austroriparian,  and  Pacific  Coast  transition  areas,  the  Austral 
region  and  wooded  slopes  of  the  Rocky  Mountains,  as  well  as 
the  humid  tropical  area. 

988.  (3.)  The  Grassland  Formation. — This   is   also   a   close 
formation,  since  the  climatic  factor,  humidity,  is  still  favorable 
to  the  abundant  growth  of  a  vegetation  type.     Here  the  vegetation 
consists  of  tufted  and  perennial  grasses  as  the  dominant  and 
potential  element,  although  other  herbage  may  exist  here  and 
there  as  an  accidental  or  subordinante  element.     This  is  the 
region  of  less  rainfall  and  high  winds,  a  transition  region  between 
the  woods  type  and  the  desert.     In  the  evolution  of  the  woods 
and  prairie  types  they  have  come  into  sharp  competition  for  the 
occupation  of  the  debatable  border  territory  with  wide  invasions 
of  each  type  into  the  interior  territory  of  the  other,  like  the  armies 
of  two  nations  struggling  for  the  occupancy  of  territory  where 
the  border  line  is  as  yet  ill-defined.     Climatic  conditions  finally 
turn  the  balance  in  favor  of  the  woods  or  prairie,  according 
as  the  degree  of  humidity  of  the  region  aids  one  above  the  other, 
and  the  border  line  becomes  established.     This  is  not  sharply 
defined  unless  there  is  some  natural  physical  barrier,  as  a  chair? 
of  mountains,  while  on  the  plain  or  level  the  transition  line 
shows  a  commingling  of  the  two  types. 

989.  (4^)  The  Desert  Formation.— Here  the  moisture  of  the 
soil  as  well  as  the  humidity  of  the  atmosphere  is  very  low  and 
the  conditions  of  life   become  so  austere  that  plants  cease  their 
conflict  with  neighbors  for  territory  because  the  conflict  with 
climate  is  so  great  as  to  keep  down  the  numbers  and  leave  un- 
occupied spaces.     Here  the  two  general  vegetation  types  (wood- 
land and  grassland)    mingle   because   there  is  plenty  of  room 
for  all  that  can  survive.     Millions  of  seeds  are  scattered  which 


5i8 


RELATION   TO   ENVIRONMENT. 


never  germinate,  or  if  they  do,  dry  up  before  they  even  get  a 
temporary  foothold.  In  the  woods  and  prairie  types  millions 
of  seeds  germinate  and  gain  temporary  hold,  only  to  be  crowded 
out  later  by  competition  among  themselves.  In  passing  from 
the  prairie  to  the  desert  there  is  a  large  transition  area,  the  plains 
where  the  formation  is  open.  It  is  neither  prairie  nor  desert 


Fig.  494. 

Desert  range  near  Mirage,  Nevada.  Open  formation,  almost  pure  salt  bush 
(Atriplex  confertifolia).  (After  Griffiths,  Bull.  38,  Bureau  Plant  Ind.,  U.  S.  Dept. 
Agr.) 

but  is  intermediate.     It  might  be  treated  of  as  a  fifth  formation, 
the  Plains  Formation. 


II.  Edaphic  Formations. 

900.  Controlling  factors. — Climatic  formations  do  not  cover 
the  entire  surface  of  the  earth  over  which  they  extend,  since 
soil  (ground)  conditions  present  limiting  factors  which  in  many 
places  overcome  the  general  climatic  influence.  The  influence 
of  different  kinds  of  soil  gives  a  more  checkered  appearance 
to  the  vegetation  because  within  climatic  regions  there  is  great 
diversity  of  soil  and  soil  conditions.  Limited  areas  are  thus 
mapped  into  small  or  large  natural  parcels.  Those  of  like  con- 
ditions, even  in  the  same  climatic  region,  are  separated  from 
each  other  by  the  intermediate  spots  of  a  different  soil  condition. 


PLANT  FORMATIONS.  519 

Each  one  of  these  limited  areas  or  spots  of  soil  furnishes  a  char- 
acteristic ecological  or  vegetation  type  of  plant  community. 
The  climatic  formations  are  thus  infiltrated,  as  it  were,  with 
plant  communities  determined  by  soil  conditions,  in  some  places 
filling  in  cavities  or  interspaces,  and  in  other  cases  actually 
intermingling  with  the  elements  of  the  climatic  types.  These 
plant  communities  are  termed  by  Schimper  edaphic  formations. 
Thus  rocky  places  or  shores,  sandy  areas  or  dunes,  certain 
swamps  or  moors,  etc.,  represent  interspaces  in  the  woods  type 
which  are  occupied  by  edaphic,  or  soil,  plant  formations. 

In  prairie  regions  where  the  ground  is  rolling,  subordinate 
herbs  may  give  the  formation  a  variegated  appearance,  i.e., 
when  Primula  officinalis  occupies  the  dry  places  and  P.  elatior 
with  differently  colored  flowers  occupies  the  damp  places.  At 
Simplon  in  dry  alpine  meadows,  Senecio  unifloris  with  large 
flowers  occurs  on  thin  soil  covering  rocks,  Senecio  incanus  occupies 
deeper  soil,  but  never  were  they  mixed.  The  hybrid  form  oc- 
cupied soil  of  an  intermediate  depth  (Schimper).  In  culture 
meadows  or  pastures  where  the  surface  of  the  ground  is  undu- 
lating the  field  is  often  covered  with  patches  of  yellow  and  white 
flowers.  In  the  low  ground  there  is  a  rich  infiltration  of  butter- 
cups (Ranunculus  acris),  and  on  the  higher  ground  of  ox-eye 
daisies  (Chrysanthemum  leucanthemum).  So  in  the  forest 
region  conditions  of  the  ground  may  be  such  as  to  modify  the 
appearance  of  the  forest,  encouraging  certain  kinds  of  trees  in 
one  locality,  others  in  another.  The  modifying  influence,  how- 
ever, is  not  sufficient  in  these  cases  to  change  the  vegetation 
type.  It  still  retains  the  climatic  character. 

991.  Open  edaphic  formations. — These  are  controlled  by  phy- 
sical or  mechanical  conditions  of  the  soil  of  such  a  nature  that 
the  struggle  for  existence  is  with  the  adverse  conditions  of  the 
ground  and  not  with  rival  plants.  The  result  is  the  same  as 
in  the  desert,  where  the  struggle  is  with  climate,  not  with  soil, 
and  there  may  be  a  mixture  of  the  elements  of  the  woods  or 
prairie  regions.  There  are  three  marked  types  of  open  edaphic 
plant  societies:  ist,  the  vegetation  of  rocky  places;  2d,  the 


RE  LA  TION   TO-   ENVIRONMENT. 


PLANT  FORMATIONS.  521 

vegetation  of  the  sandy  beach  or  strand;   3d,  the  vegetation  of 
the  "bad  lands"  and  alkali  marshes. 

992.  Close  edaphic  formations. — While  these  are   controlled 
by  conditions  of  the  ground,  these  conditions  are  not  so  austere 
as  to  prevent  the  development  of  a  close  growth.     In  the  forest 
region  too  much  water  in  the  soil  may  prevent  forest  growth,  but 
encourages  a  rank  growth  of  marsh  plants.     Some  of  the  ex- 
amples of  close  edaphic  formations  are:  ist,  mud  or  reed-swamp 
formations;     2d,    meadow-swamp    formations;     3d,    sphagnum 
moor  formations.     The  "park-like  forests"  along  river  bottoms 
in  the  prairie  region  or  the  "oases"  in  deserts  are  close  edaphic 
formations  in   these   regions,  since  they  are  not  developed  in 
response  to  the  climate,  but  in  response  to  a  condition  of  the 
ground   (the  abundance  of  ground  water),   although  the  type 
of  the  vegetation  is  really  that  of  the  forest. 

III.  Aquatic  Formations. 

993.  These  are  represented  by  the  vegetation  in  ponds,  lakes, 
streams,  and  in  the  ocean.     The  vegetation  is  of  a  type  very 
distinct  from  the  climatic  or  edaphic.     The  formations  occur 
as  patches  or  strips  infiltrated  in  the  climatic  and  edaphic  for- 
mations, and  also  as  a  fringe  along  continents,  islands,  or  bodies 
of  land  bordering  deep  and  large  bodies  of  water.     The  character 
of  the  vegetation  is  hydrophytic  or  halophytic,  according  to  its 
occurrence  in  fresh  water  or  salt  water.     There  are,  therefore, 
two  grand  subdivisions:    ist,  fresh  water  or  limnetic  formations; 
2d,  salt  water  or  pelagic  formations. 

IV.  Culture  Formations. 

994.  This  type  of  vegetation  is  developed  in  response  to  the 
work  of  man  in  the  cultivation  of  the  soil,  or  as  a  result  of  his 
interference  with  the  development  of  the  climatic  type  of  vege- 
tation.    Man  overcomes  the  climatic  factor  by  removal  of  the 
climatic  vegetation  type  and  by  the  cultivation  of  the  soil;    in 


522  RELATION    TO   ENVIRONMENT. 

arid  regions  by  irrigation  in  addition  to  cultivation.  In  a  broad 
sense  there  are  two  general  types  of  the  culture  formations: 
ist,  the  vegetation  of  cultivated  fields;  2d,  the  vegetation  of 
waste  places.  There  is  not  space  in  this  book  even  for  a  satis- 
factory outline,  and  no  discussion  of  these  formations  will  be 
given.  Only  a  few  of  the  prominent  culture  formations  will 
be  mentioned  at  this  place. 

995.  Vegetation  of  cultivated  fields. — Here  belong  the  field 
and  garden  crops.    Examples:  the  cereals  (wheat,  etc.),  corn,  rice, 
potatoes,  meadow  grasses,  pastures,  cotton,  cane,  beans,  beets, 
orchard   fruits,   berries,    vegetables,   gardens   of   various   kinds, 
and  forests  in  some  cases. 

995a.  Vegetation  of  waste  places. — This  would  include  ground 
once  cultivated  or  cleaned  and  later  abandoned  for  the  time  or 
devoted  to  other  purposes.  Examples:  the  vegetation  of  road- 
sides and  road  embankments,  of  abandoned  fields,  of  yards  or 
areas  not  devoted  for  the  time  to  agricultural  or  horticultural 
purposes.  The  plants  growing  in  such  places  are  usually  called 
"weeds,"  though  "weeds"  are  often  very  abundant  in  culture 
formations  and  sometimes  develop  to  such  an  extent  as  to  en- 
tirely overcome  them. 

V.  Principal  and  Individual  Formations. 

996.  The   principal   formations. — The    term    formation,    or 
principal  formation,  is  used  by  some  in  speaking  of  the  dominant 
vegetation  of  places  more  or  less  limited  by  distinct  physiographic 
areas.     In  this  sense  the  formation,  or  principal  formation,  is 
not  very  different,  if  at  all,  from  a  single  edaphic  formation,  or 
single  water  formation.     It  is  made  up  of  the  different  individual 
formations   which   are   the   dominant   vegetation   forms   in   the 
zones  or  plats  which  are  usually  present  on  different  portions 
of  the  same  physiographic  area. 

997.  Plant   societies. — The   term   plant   society  is   used   by 
some  in  a  broad  sense  to  include  all  those  plants  living  together 
over  an  area  possessing  a  nearly  or  quite  uniform  ground  con- 


PLANT  FORMATIONS.  $2$ 

dition  and  environment.  Ground  is  here  used  in  a  broad  sense 
to  mean  the  earth  substratum  in  or  upon  which  the  plants  grow, 
and  includes  water  areas  as  well  as  land  areas.  In  this  sense 
different  plant  societies  occupy  somewhat  distinct  physiographic 
areas,  as  marsh,  moor  (or  bog),  strand,  rocky  areas,  sandy 
areas,  ponds,  lakes,  etc.  These  areas  may  be  quite  limited 
in  size,  or  they  may  cover  many  thousands  of  square  miles. 
The  territory  of  a  plant  society,  then,  is  in  many  cases  coincident 
with  the  territory  of  a  single  area  of  the  edaphic  formation,  or 
equivalent  to  the  area  of  a  principal  formation.  But  the  term 
society  is  generally  used  in  a  broader  sense  than  formation,  which 
refers  more  to  the  dominant  vegetation. 

998.  The  individual  formation.— In  each  plant  society,  while 
the  general  aspect  of  the  vegetation  is  the  same,  there  are  certain 
limiting  factors  which  give  it  a  more  or  less  variegated  appear- 
ance. These  factors  are  of  two  kinds:  ist,  the  physical,  which 
relate  to  the  variation  in  ground  water,  and  to  physical  and 
chemical  conditions  of  the  soil;  and  2d,  biological,  which  relate 
to  the  struggle  between  different  species  to  occupy  the  same 
patch  of  ground.  Distinct  groups  of  vegetative  elements  are 
thus  formed  in  a  society  because  in  certain  more  or  less  limited 
areas  one  or  several  species  are  dominant  and  give  a  charac- 
teristic physiognomy  to  the  area.  Such  a  group  in  a  society  is 
called  a  formation.*  In  reality  the  different  formations  re- 
semble pieces  of  mosaic,  when  arranged  without  order,  or  zones 
when  arranged  regularly  where  there  is  radial  or  lateral  topo- 
graphic symmetry.  This  is  well  illustrated  in  certain  marshes, 
or  in  shallow  water,  along  margins  of  lakes,  where  there  are 

*  Formation  is  used  in  this  sense  by  some,  while  others  use  here  the 
term  association,  reserving  the  term  formation  for  a  group  of  associations, 
i.e.,  a  principal  formation.  But  the  term  association  itself  does  not  seem 
well  chosen.  The  word  seems  more  applicable  to  certain  "associations" 
in  a  society  or  formation,  i.e.,  certain  of  the  subordinate  members  (ex- 
ample, lianas,  epiphytes,  or  other  subordinate  members).  Some  even  pro- 
pose the  word  society  for  epiphytes  and  lianas,  and  cite  Schimper's  use 
of  it  in  this  connection.  Schimper  uses  for  epiphytes  the  term  Genos- 
senschaft,  which  means  rather  an  association  or  guild. 


524  RELATION   TO   ENVIRONMENT. 

often  extensive  patches  *  or  areas  of  the  cat-tail  flag,  which  ap- 
pears at  a  little  distance  to  occupy  the  area  to  the  exclusion  of 
all  other  vegetation.  In  similar  locations  are  patches  of  arrow- 
leaf,  of  rushes,  reed  grasses,  etc.  In  low  damp  ground  near 
bodies  of  water  or  streams,  the  alders  and  willows  often  form 
each  a  distinct  patch  or  zone.  In  forests  there  are  often  dis 
tinct  groups  of  white  pine  or  of  pitch  pine,  sometimes  of  maple 
or  beech.  Smaller  plants  are  often  between  the  larger  ones 
composing  these  groups,  or  in  their  shade,  but  the  larger  plants 
so  closely  associated  are  dominant  and  characterize  the  area. 

The  various  groups  above  described  would  then  be  called  cat- 
tail-flag formation  (or  Typha  formation),  arrow-leaf  formation 
(Sagittaria  formation),  Cassandra  formation,  white-pine  for- 
mation, etc.  (The  same  formations  are  sometimes  called  also 
typhetum,  sagittarietum,  cassandretum,  pinetum,  etc.)  In  the 
cases  just  cited  above,  a  single  species  is  dominant,  and  it  is 
a  pure  formation.  In  many  cases  the  individuals  of  several 
species  may  share  the  same  spot  or  area  of  ground  equally  or 
nearly  so.  In  the  former  case  the  individuals  of  the  one  species 
are  able,  in  their  competition  with  others,  to  occupy  the  ground 
to  the  exclusion  of  their  competitors,  either  because  they  possess 
characters  which  enable  them  to  gain  the  upper  hand,  or  be- 
cause competing  species  may  not  have  been  present  at  the 
start.  When  the  individuals  of  several  species  occupy  equally 
the  same  ground,  the  formation  is  mixed.  The  conditions  are 
favorable  for  the  growth  of  several  dominant  species,  and  all, 
as  it  were,  feed  at  the  same  table,  with  no  greater  competition 
between  the  individuals  of  several  species  than  there  would 
be  between  the  individuals  of  one  species  were  only  one  species 
present.  This  mixture  of  several  species  of  the  same  grade 
of  dominance  is  sometimes  called  commensalism,  and  the  term 
is  also  extended  to  mixtures  where  individuals  of  smaller  species 
are  mixed  in  between  those  of  larger  ones  or  in  their  shade, 
and  do  not  come  into  actual  competition  with  them.  Examples 


*  All  small  patches  should  not  be  regarded  as  a  formation. 


PLANT  FORMATIONS.  525 

of  mixed  formations  are  seen  in  the  mixture  of  joepye-weed 
and  boneset  in  low  ground.  This  would  then  be  a  joepye-weed- 
boneset  formation.  Each  of  these,  however,  often  grows  sepa- 
rately, and  then  would  form  pure  formations.  In  the  forest, 
beech,  birch,  and  maple  are  sometimes  mixed,  forming  a  beech- 
birch-maple  formation.  Again,  oaks,  beech,  maple,  and  hem- 
lock may  form  an  oak-beech-maple-hemlock  formation,  and 
so  on,  which  may  vary  in  different  patches  of  an  area,  even 
where  the  general  conditions  are  the  same,  and  the  name  of 
the  formation  would  vary  accordingly.  Besides  the  dominant 
species  of  a  formation  there  are  subordinate  species  which  may 
not  be  prominent  enough  to  change  its  aspect,  but  at  most  only 
modify  it. 

999.  Fades. — The  term  jades  is  sometimes  applied  to  each 
of  the  dominant  species  in  a  formation.     Where  there  is  but  one 
dominant  species  there  is  a  single  facies;   where  there  are  several 
dominant  species  in  a  formation  each  one  is  a  facies. 

1000.  Vegetation  forms. — Vegetation  form  refers  to  the  special 
ecological   form   which   individual   species  of  a   formation   take 
under  the  conditions,  without  regard  to  the  importance  of  the 
species  in  the  formation.     One  or  several  vegetation  forms  may 
be  dominant  (these  would  constitute  the  facies  of  the  formation), 
while  others  are  subordinate  or  even  inconspicuous. 

1001.  Layers. — By  layers  is  meant  the  different  strata  in  a 
formation  or  society.     While  these  are  present  to  some  extent 
in  nearly  all  plant  societies,  they  are  more  marked  in  the  forest 
societies.     The  forest  trees  because  of  their  greater  height  form 
a  canopy  which  shades  the  interior.     The  tall  trees  constitute, 
therefore,  the  upper  layer.     Large  shrubs  growing  in  the  forest 
would    constitute   a   second   layer,    small   shrubs   a   third   layer, 
herbaceous  plants  a  fourth,  mosses,  lichens,  etc.,  on  the  ground 
a  fifth,  and  so  on.     The  layers  may  in  some  cases  be  even  more 
numerous. 

1002.  Zones. — Applied  to  vegetation  this  refers  to  lateral  layers 
so  clearly  shown  where  there  is  radial  or  lateral  topographic 
symmetry. 


526 


RELATION   TO   ENVIRONMENT. 


GENERAL 
FORMATIONS. 


1003.  Summary  of  formations. 

I.  Climatic  (controlled  by  climatic  factors). 

1.  The  woods  or  forest  formation. 

2.  The  prairie  formation. 

3.  The  plains  formation. 

4.  The  desert  formation. 

5.  The  arctic-alpine  formations. 

II.  Edaphic  (controlled  by  ground  factors). 

6.  Edaphic  or  soil  plant  formations. 

a.  Rocky  places. 

b.  Sand  areas. 

c.  Marshes,  moors,  meadows. 

d.  Alkaline  areas,  etc. 

III.  Aquatic  (controlled  by  bodies  of  water). 

7.  The  aquatic  formations. 

a.  Fresh-water  formations. 

b.  Salt-water  formations. 

IV.  Culture  (controlled  by  man). 

8.  The  culture  formations. 

a.  Cultivated  areas. 

b.  Waste  places. 

PRINCIPAL  FORMATION   (society]    (controlled  chiefly  by  distinct 

physiographic  areas). 

1.  Layered. 

2.  Zoned. 

3.  Built  up  of  vegetation  forms. 
Individual  Formations   (controlled   by  physical  and  biological 

factors). 

1.  Layered. 

2.  Zoned. 

(One    or    several    facies    make    up    the 
formation). 

1004.  The  terminology  of  plant  communities  is  at  present  in 
a  very  unsettled  state,  and  it  is  necessary  for  nearly  every  writer 
to  define  the  terms  and  the  limits  of  their  application.     Without 


PLANT  FORMATIONS,  S27 

attempting  to  decide  what  system  of  terminology  should  be  used, 
the  author  feels  it  is  best  in  this  treatise  for  elementary  use  to 
employ  the  terminology  given  above.  The  discussions  here  will 
center  on  the  society,  since  it  is  believed  that  it  will  be  more 
useful  in  this  elementary  work  to  treat  the  subject  rather  from 
the  broad  standpoint  of  the  plant  society,  showing  the  interrela- 
tion of  members  of  different  grades  and  the  general  relation  of 
dominant  members  to  environment.  The  various  systems  used 
by  different  writers  can  be  found  in  their  works  listed  at  the  close 
of  this  part. 

1005.  Complex  character  of  plant  societies. — In  their  broadest 
analysis  all  plant  societies  are  complex.  Every  plant  society  has 
one  or  several  dominant  species,  the  individuals  of  which,  because 
of  their  number  and  size,  give  it  its  peculiar  character.  The 
society  may  be  so  nearly  pure  that  it  appears  to  consist  of  the 
individuals  of  a  single  species.  But  even  in  those  cases  there  are 
small  and  inconspicuous  plants  of  other  species  which  occupy 
spaces  between  the  dominant  one.  Usually  there  are  several  or 
more  kinds  in  the  same  society.  The  larger  individuals  come 
into  competition  for  first  place  in  regard  to  ground  and  light,  the 
smaller  ones  come  into  competition  for  the  intervening  spaces 
for  shade,  and  so  on  down  in  the  scale  of  size  and  shade  tolerance. 
Then  climbing  plants  (lianas),  and  epiphytes  (lichens,  algae, 
mosses,  ferns,  tree  orchids,  etc.),  gain  access  to  light  and  support 
by  growing  on  other  larger  and  stouter  members  of  the  societT  , 
(See  evergreen  tropical  forests,  Chapter  L.) 

Parasites  (dodder,  mistletoes,  rusts,  smuts,  mildews,  bacteria, 
etc.)  are  present,  either  actually  or  potentially,  in  all  societies,  and 
in  their  methods  of  obtaining  food  sap  the  life  and  health  of  their 
hosts.  Then  come  the  scavenger  members,  whose  work  it  is  to 
clean  house,  as  it  were,  the  great  army  of  saprophytic  fungi 
(molds,  mushrooms,  etc.),  and  bacteria  ready  to  lay  hold  on  dead 
and  dying  leaves,  branches,  trunks,  roots,  etc.,  disintegrate  them, 
and  reduce  them  to  humus  where  other  fungi  change  them  into  a 
form  in  which  the  larger  members  of  the  plant  society  can  utilize 
them  as  plant  food  and  thus  continue  the  cycle  of  matter  through 


528  RELATION    TO   ENVIRONMENT. 

life,  death,  decay,  and  into  life  again.  Mycorhiza  (see  Chapter  IX) 
or  other  forms  of  mutualistic  symbiosis  occur  which  make  atmos- 
pheric nitrogen  available  for  food,  or  shorten  the  path  from  humus 
to  available  food,  or  the  humus  plants  feed  on  the  humus  directly. 
Nor  should  we  leave  out  of  account  the  myriads  of  nitrate  and 
nitrite  bacteria  (see  Chapter  IX)  which  make  certain  substances  in 
the  soil  available  to  the  higher  members  of  the  society.  Most 
plant  societies  are  also  benefited  or  profoundly  influenced  in 
other  ways  by  animals,  as  the  flower-visiting  insects,  birds  which 
feed  on  injurious  insects,  the  worms  which  mellow  up  the  soil  and 
cover  dead  organic  matter  so  that  it  may  more  thoroughly  decay. 
In  short,  every  plant  society  is  a  great  cosmos  like  the  Universe 
itself  of  which  it  is  a  part,  where  multitudinous  forms,  processes, 
influences,  evolutions,  degenerations,  and  regenerations  are  at 
work. 


CHAPTER  L. 

FOREST   SOCIETIES. 

1.  General  Character  of  Forest  Societies. 

1006.  Extent  of  forest  societies. — Forests  represent  the  highest 
stage  of  evolution  in  plant  communities.     Some  forests  represent 
also  the  most  complex  stage.     In  their  distribution  forests  range 
from  the  tropics  to   subarctic  regions,  from  wet  and  marshy  low- 
lands to  high  mountain  altitudes,  and  they  are  also  transconti- 
nental.    Their   farthest   north   is   limited   by   arctic   cold,    their 
highest  altitude  by  alpine  cold  and  winds,  their  breadth  of  distri- 
bution by  bodies  of  water,  by  wind,  and  by  desert  conditions.     The 
forest  is  the  climax  type  in  the  evolution  of  plant  communities, 
and  the   only  hindrance  to  complete  occupation  of  the  land  are 
exteme  cold,  dryness,  frequent  and  severe  winds  and  fire,  and 
the  needs  of  human  civilization. 

1007.  Complexity  of  forest  societies.— All  plant  communities  are 
more  or  less  complex,  but  the  forest  type  is  the  most  complex  of  all. 
This  is  due  to  the  fact  that  in  the  forest  there  is  the  greatest  diver- 
gence among  its  members  in  point  of  style,  form,  character  and 
work.    The  abundance  of  the  tree  type  stamps  the  community  as 
a  forest.    Trees  are  the  largest  plants.     The  bacteria,  abundant  in 
all  aerated  soils  and  in  decaying  vegetation,  represent  the  smallest 
individuals.     Between  these  two  extremes  there  are  gradations  in 
size,  form,  habit,  and  habitat,  in  the  forest  society.     The  forest 
teems  with  many  kinds  of  algee,  fungi,  lichens,  mosses,  ferns,  herbs, 
undershrubs   and   other   shade   plants,    epiphytes,    etc.,    to    say 

529 


53O  RELATION   TO   ENVIRONMENT. 

nothing  of  the  great  variety  of  animal  life.  Some  forests  are  more 
complex  than  others.  Because  of  the  great  divergence  of  form, 
character,  and  work  among  the  members  of  a  forest  society,  it  is 
one  of  the  most  interesting  ones  for  study. 

1008.  Different  kinds  of  forests. — We  know  that  the  con- 
stituents of  a  plant  community  vary.     Not  only  is  there  variation 
in  different  years  or  periods,  there  is  variation  in  different  regions. 
Regions  which  are  so  widely  separated  as  to  show  great  climatic 
differences  show  great  differences  in  the  character  of  plant  com- 
munities.    The  same  is  true  of  the  forest.     Each  different  climatic 
belt  or  region  has  its  characteristic  forest.    For  example,  the  forests 
of  the  Hudsonian  zone  in  North  America  are  different  from  those 
of  the  Canadian  zone,  and  these  in  turn  different  from  those  in 
the  Transition  zone.     The  forests  of  the  Rocky  Mountains  and 
of  the  Pacific  coast  differ  from  those  of  the  Alleghanian,  Carolinian, 
or    Austroriparian    areas,    because    there    are    natural    barriers 
extending  north  and  south  in  addition  to  the  transcontinental  bio- 
thermal  barriers.     Finally,  tropical  forests  are  strikingly  differ- 
ent from  those  of  other  regions.     Similar  variations  occur  in  the 
forests  of  other  regions  of  the  globe.     The  character  of  these 
forests  depends  largely  on  climatic  factors.     The  character  of  the 
forest  varies,  however,  even  in  the  same  climatic  area,  dependent 
on  soil  conditions,  or  success  in  seeding  and  ground-gaining  of  the 
different  species  in  competition,  etc. 

1009.  Thickets. — According  to  Schimper  thickets  belong  to 
the  woodland  climatic  type  of  vegetation  (see  Chapter  XLIX). 
Thickets  are  dense  formations  of  shrubs.     Warming  says  they 
are   the  "  unsuccessful    attempt    of   nature   to   form  a   forest." 
Examples  in  our  country  are   the   thickets  of    willows,  alders, 
hazels,  etc.,  found  in  the  eastern  and  northern  parts  of  North 
America,   and  the    "  chaparral "    in    the    southwestern    United 
States  in  the  arid  regions.      Here  these   " chaparral"   thickets 
are   often   composed   of   the   mesquite,    mimosas,    acacias,    etc. 
The  highest  type  of  thicket,  however,  is  developed  in  some  of 
the  tropical  or  subtropical  regions,  especially  of  Africa,  where 
the  climate  is  rather  severe,  there  being  a  long  dry  season  alternat- 


FOREST  SOCIETIES.  531 

ing  with  a  rainy  season.  These  thickets  are  very  highly  devel- 
oped in  the  so-called  " thorn  woods"  and  are  often  impenetrable 
because  of  the  very  dense  and  intricate  growth,  often  with  a  pro- 
fuse development  of  thorns.  In  the  southern  Appalachians  in 
North  America  very  dense  thickets  are  sometimes  formed  by 


Fig.  4960. 

Forest  with  chaparral,  southwestern  United  States.  (Bureau  of  Forestry, 
U.  S.  Dept.  Agr.) 

the  rhododendrons,  which  here  reach  such  a  high  development, 
especially  R.  maximum. 

1010.  General  structure  of  the  forest. — Structurally  the  forest 
possesses  three  subdivisions:  the  floor,  the  canopy,  and  the  in- 
terior. The  floor  is  the  surface  soil,  which  holds  the  rootage 
of  the  trees,  with  its  covering  of  leaf-mold  and  carpet  of  leaves, 
mosses,  or  other  low,  more  or  less  compact  vegetation.  The 
canopy  is  formed  by  the  spreading  foliage  of  the  tree-crowns, 
which,  in  a  forest  of  an  even  and  regular  stand,  meet  and  form  a 
continuous  mass  of  foliage  through  which  some  light  niters  down 
into  the  interior.  Where  the  stand  is  irregular,  i.e.,  the  trees  of 


532  RELATION    TO   ENVIRONMENT. 

different  heights,  the  canopy  is  said  to  be  " compound"  or 
"storied."  Where  it  is  uneven,  there  are  open  places  in  the 
canopy  which  admit  more  light,  in  which  case  the  undergrowth 
may  be  different.  The  interior  of  the  forest  lies  between  the 
canopy  and  the  floor.  It  provides  for  aeration  of  the  floor  and 
interior  occupants,  and  also  room  for  the  boles  or  tree  trunks 
(called  by  foresters  the  wood  mass  of  the  forest)  which  support 
the  canopy  and  provide  the  channels  for  communication  and 
food  exchange  between  the  floor  and  canopy.  The  canopy 
manufactures  the  carbohydrate  food  and  assimilates  the  min- 
eral and  proteid  substances  absorbed  by  the  roots  in  the  soil; 
and  also  gets  rid  of  the  surplus  water  needed  for  conveying  food 
materials  from  the  floor  to  the  place  where  they  are  elaborated 
It  is  the  seat  where  energy  is  created  for  work:  and  also  the 
place  for  seed  production. 

1011.  Longevity  of  the  forest. — The  forest  is  capable  of  self- 
perpetuation,  and  except  in  case  of  unusual  disaster  or  the  action 
of  man,  it  should  live  indefinitely.     As  the  old  trees  die  they 
are  gradually  replaced  by  younger  ones.     So  while  trees  may 
come  and  trees  may  go,  the  forest  goes  on  forever. 

1012.  Longevity  of  the  tree. — Trees,  like   nearly  all  organ- 
isms, pass  through  the  stages  of  growth  and  senescence,   and 
then  die.     What  it  is  which  inhibits  the  growth  of  trees  at  a  cer- 
tain stage,  and  later  brings  about  death,  is  not  known.     The 
entire  tree  is  surrounded  by  a  layer  of  growing  tissue  (cambium). 
The  branches  and  roots  are  extended  in  length  by  increase  of 
this  tissue  at  the  "  growing  points,"  while  the  trunk,  branches, 
and  roots  are  increased  in  diameter  by  the  growth  of  the  cylinder 
of  cambium  underneath  the  bark,  which  adds  each  year  a  layer 
outwardly  to  the  bark  and  a  layer  inwardly  to  the  wood.     Thus, 
each  year,  new  embryonic  tissue;    new  channels  for  conduction 
of  food;    new  organs  for  absorption,   for  respiration,   and  for 
photosynthesis,    assimilation,    transpiration,    reproduction,    etc., 
are  formed.     For  this  reason  some  have  suggested  there  is  no 
reason  why  the  tree  should  not  live  forever,  barring  accidents. 
But,  when  trees  reach  a  certain  height,  increase  in  height  ceases, 


FOREST  SOCIETIES. 


533 


or  is  so  slight  as  to  be  practically  imperceptible.  Here  the  tree 
may  stand  for  a  long  time,  but  it  finally  dies.  Some  have  sug- 
gested that  certain  natural  forces  inhibit  or  set  a  limit  to  growth 
in  height,  as  wind  for  example.  But  trees  in  protected  valleys 
do  not  go  on  increasing  in  height  beyond  the  normal  height 
for  the  species.  Certain  trees  like  the  mangrove  or  banyan, 


Fig.  4966. 

Banyan  tree  moved  in  one  direction  by  trade  wind.     The  older  portion  of  the 
tree  is  at  the  right. 

which  spread  by  branches  growing  down  into  the  ground,  may 
live  indefinitely,  but  the  older  trunks  finally  die.  The  banyan 
tree  in  windy  exposures  develops  to  the  leeward,  and  in  time 
the  old  trunk  may  thus  travel  considerable  distances.  Trees 
finally  die  of  "old  age."  In  nearly  all  organisms  growth  is  at 
first  slow,  then  is  accelerated,  reaches  a  maximum,  then  the  rate 
of  growth  declines,  and  finally  ceases,  when  life  may  be  main- 
tained for  years  with  no  perceptible  increase  in  size,  but  a  gradual 
waste  and  lessening  in  energy  and  vitality,  until  finally  death 
ensues.  This  is  in  the  later  stages  often  accelerated  by  para- 
sitic organisms  which  take  advantage  of  the  weakened  constitu- 
tion, if  the  tree  does  not  in  the  mean  time  fall  before  the  force 
of  the  wind.  Many  trees  live  for  several  centuries.  A  few 


J, 


534  RELATION    TO   ENVIRONMENT. 

trees  are  known  which  have  lived  several  thousand  years.  A  It 
is  said  there  is  in  Kent,  England,  a  tree  of  the  genus  Taxus,  3000 
years  old;  also  that  there  are  now  living  on  the  slopes  of  Mt.  ^Etna 
chestnut  trees  from  which  Homer  might  have  gathered  nuts; 
in  southern  Mexico  there  is  an  old  cypress  tree  (Taxodium) 
believed  to  be  about  6000  years  old,  and  in  the  Cape  Verde 
Islands  an  Adansonia  of  similar  age.  Another  account  states 
that  this  old  cypress  in  Mexico  is  about  2500  years  old.  It  is 
difficult  to  get  accurate  data  concerning  trees  of  such  age,  but 
in  the  case  of  the  Big  trees  of  California  (Sequoia  washing- 
toniana)  data  have  been  obtained  by  counting  the  annual  rings 
of  a  number  of  trees  which  shows  their  age  to  range  up  to  4000 
years,  f 

II.  Boreal  Forests. 

The  Boreal  forests  of  North  America  form  transcontinental 
belts  and  according  to  biothermal  lines  are  in  two  zones. 

1013.  Forests  of  the  Hudsonian  zone. — These  are  the  north- 
ernmost of  the  forests,  extending  from  Labrador  to  Alaska, 
reaching  the  farthest  north  of  tree  growth,  and  extending  south- 
ward on  the  upper  timbered  slopes  of  the  mountain  ranges  of 
the  United  States  and  Mexico.  The  trees  are  mainly  spruces  and 
firs,  with  here  and  there  colonies  and  mixtures  of  birches  and 
aspens.  The  conifers,  especially  the  spruces,  firs,  and  balsams, 
are  better  adapted  to  growing  at  low  temperatures  than  other 
trees,  and  this  is  why  we  find  them  pushing  so  far  into  the  cold 
of  the  north  or  that  of  high  mountain  altitudes.  The  leaves 
are  small,  comparatively  thick,  and  with  a  thick  cuticle  which 
retards  transpiration.  This  is  necessary  on  account  of  the 
high  winds,  which  increase  the  loss  of  water,  and  the  cold  soil, 
which  retards  absorption.  The  conical  form  of  the  tree  dis- 
tributes the  weight  of  snow  more  evenly,  so  that  the  danger  of 
breaking  is  lessened,  while  the  tops  offer  less  resistance  to  the 
wind,  which  is  more  severe  in  these  regions.  The  higher  mountain 
peaks  in  the  northern  Alleghanian  and  in  the  Rocky  Mountains 


FOREST  SOCIETIES.  535 

are  occupied  by  an  arctic-alpine  flora  of  mosses,  lichens,  heaths, 
etc.,  or  the  higher  ones  are  snow-clad,  while  in  the  southern  Alle- 
ghanies  the  highest  mountains  are  often  clad  to  the  summit  with 
spruces  and  firs  (balsam).  Mt.  Mitchel,  in  North  Carolina,  the 
highest  mountain  (6711  ft.)  east  of  the  Rockies,  is  clothed  to  the 
summit  with  spruces  and  firs,  while  pines  and  deciduous  trees 
are  on  its  slope.  \ 

1014.  Forests  of  the  Canadian  zone. — The  forests  of  the  Ca- 
nadian zone  are  similar,  but  have  some  species  which  do  not 
reach  so  far  north  as  the  spruces  and  firs,  especially  some  of  the 
pines,  the  hemlock,  spruce,  and  deciduous  trees,  but  the  conifers 
outnumber  the  latter. 

III.  Austral  Forests. 

1015.  The  forests  of  the  Austral  region  show  greater  varia- 
tions arid  do  not  form  transcontinental  belts  because  of  the  barriers 
presented  by  the  arid  interior  portion  of  the  United  States,  the 
high  Rockies,  and  probably  because  of  the  peculiar  temperature 
conditions  of  the  Pacific  coast,  where  a  "  low  summer  temperature 
combined  with  a  high  sum  total  of  heat"  permits  a  wider  range 
and  mixing  north  and  south  of  boreal  and  austral  types. 

1016.  Deciduous  forests  of  Alleghanian  and  Carolinian  areas. 
— The  highest  development  of  the  deciduous  forest  in  North 
America  is -in  the  Austral  region,  principally  in  the  humid  Alle- 
ghanian and  Carolinian  areas  of  the  same.     In  the  former  are  the 
oaks,   hickories,   chestnuts,   locusts,   ashes,   birches,   aspens,   the 
northern   spruces,  firs,  hemlocks,   pines,   and   other   coniferous 
trees  found  farther  south.      In    the  latter  are  the    tulip-tree  or 
whitewood,   cucumber-tree,  persimmon,   sweet  gum,   sourwood, 
chestnut  oak,  Spanish  oak,  and  yellow  and  scrub  pine. 

1017.  Autumn  colors. — One  of  the  striking  effects  produced 
by  the  deciduous  forests  is  that  of  the  autumn  coloring  of  the  leaves. 
It  is  more  pronounced  in  the  forests  of  the  United  States  than  in 
corresponding  life  zones  in  the  eastern  hemisphere  because  of  the 
greater  number  of  species.     With  the  disintegration  of  the  chloro- 


536  RELATION   TO   ENVIRONMENT. 

phyll  bodies,  other  colors,  which  in  some  cases  were  masked  by 
the  green,  appeal.  In  other  cases  decomposition  products  result 
in  the  formation  of  other  colors,  as  red,  scarlet,  yellow,  brown, 
purple,  maroon,  etc.,  in  different  species.  These  coloring  sub- 


Fig.  497. 

Conifers  overtopping  broad-leaved,  deciduous  trees  in  the  forest  (New  Hamp- 
shire).    A  "mixed"   forest. 

stances  to  some  extent  are  believed  to  protect  the  nitrogenous  sub- 
stances in  the  leaf  from  injury.  The  colors  absorb  the  sun's  rays, 
which  otherwise  might  destroy  these  nitrogenous  substances  before 
they  have  passed  back  through  the  petiole  of  the  leaf  into  the  stem, 
where  they  may  be  stored  for  food.  The  gorgeous  display  of  color, 
then,  which  the  leaves  of  many  trees  and  shrubs  put  on  is  one  of 
the  many  useful  adaptations  of  the  plants. 


FOREST  SOCIETIES. 


537 


1018.  Forests  of  the  Austroriparian,  or  Louisianian,  area. — 

There  are  two  distinct  types  of  forest:  ist.  The  upland  forest, 
occupying  the  dry,  higher  ground,  is  characterized  by  the  long- 
leaf  and  loblolly  pines,  the  live-oak,  magnolia,  and  palmetto. 
2d.  The  palustrine  forest  occupies  the  swamps  of  the  coastal  plain 
of  the  South  Atlantic  and  Gulf  States,  and  the  lowlands  of  the 
rivers,  extending  from  Hampton  Roads  and  Chesapeake  Bay 


Fig.  4Q8a. 
Cypress  knees,  Mississippi.     (Photograph  by  H.  von  Schrenk.) 

in  southeastern  Virginia,  reaching  inland  for  some  distance 
along  the  principal  rivers  of  the  region,  and  then  extending  up  the 
Mississippi  River  and  its  main  tributaries  to  Missouri  and  southern 
Illinois  and  Indiana.  In  this  area  the  seaward  slope  from  early 


538  RELATION   TO  ENVIRONMENT. 

times  was  slight,  and  the  vegetation  retarded  the  flow  of  water  to 
a  much  greater  extent  than  on  a  more  pronounced  incline.  This, 
together  with  the  effect  of  the  sands  in  damming  up  to  some  extent 
the  flow,  has  produced  the  conditions  which  have  made  this  great 
swamp  possible.  Some  of  the  characteristic  vegetation  growing 
in  the  area  is  especially  effective  in  retarding  the  flow  of  the 
drainage  water  from  the  surface  and  higher  elevations,  the  cane 
(Arundinaria),  the  bald  cypress,  the  tupelo  gum,  in  some  places 
the  mangrove,  etc.  The  bald  cypress  in  wet  ground  develops 
numerous  erect  "knees"  (fig.  4980)  from  the  roots,  which  serve 
the  purpose  of  aerating  the  root  system,  and  they  also  catch 
floating  material. 

1019.  Forests  of  the  Pacific  transition  area.— This  is  a  majes- 
tic coniferous  forest,  in  parts  of  Washington,  Oregon,  and  Califor- 
nia, due  to  the  unusual  conditions  which  prevail.     The  annual 
rainfall  is  very  heavy.     The  principal  trees  are  the  Douglas  fir, 
Pacific  cedar,  western  hemlock,  and  Sitka  spruce,  whose  trunks 
gain  an  average  height  of  more  than  200  feet.     Altogether  in 
Washington  and  Oregon  there  are  27  different  species  of  conifer- 
ous trees.     Some  of  those  not  mentioned  above  are  the  western 
white  pine,  the  giant  redwood,  and  the  Big  trees  of  California. 
Broad-leaved  trees,  as  maples,  birches,  oaks,  aspens,  alders,  madro- 
nas,  western  dogwoods,  and  different  kinds  of  shrubs,  many  of 
them  reaching  the  size'of  small  trees,  occur  as  undergrowth  which 
often  chokes  the  interior  of  the  forest,  while  the  forest  floor  in 
many  places  is  carpeted  with  mosses  and  ferns.  " 

1020.  The  redwood  (Sequoia  sempervirens)  reaches  a  greater 
height  than  any  other  American  tree,*  but  does  not  attain  the 
age  of  the  Big  tree  of  the  Sierra  Mountains  in  California.     The 
redwood  is  confined  to  a  "narrow  strip  of  the  coast  ranges  10  to 
30  miles  wide  extending  from  the  Bay  of  Monterey,  CaL,  to  a 
short    distance    across    the    southern    border   of    Oregon."     On 
mountain  slopes  it  reaches  a  maximum  height  of  about  225  feet 
and  10  feet  in  diameter,  while  in  the  valleys,  where  soil  and  moist- 


*  According  to  R.  T.  Fischer. 


FOREST  SOCIETIES. 


539 


ure  conditions  are  better,  it  attains  a  height  of  3  50  feet  by  20  feet  in 
diameter.  When  the  tree  has  reached  the  age  of  500  years  it 
usually  begins  to  fall  off  in  growth  and  die  downward  from  the 
top.  The  oldest  redwood  found  by  the  investigations  of  the 
United  States  Forestry  Division  in  1899  and  1900  was  1373 
years  old.  Lumbering  the  redwood  is  now  confined  to  the 
northern  counties  in  California;  the  stands  in  Santa  Cruz  are 


Fig.  4986. 

Mature  forest  of  redwood  (Sequoia  sempervirens).  (Bureau  of  Forestry,  U.  S. 
Dept.  Agr.,  Bull.  38.) 

to  be  made  up  into  a  park,  while  smaller  stands  are  left  in  other 
portions  of  the  range. 

1021.  The  Big  tree  (Sequoia  washingtoniana)  now  occurs 
in  scattered  groves  along  the  west  slope  of  the  Sierra  Nevada 
Mountains  a  distance  of  260  miles  from  the  head  of  Deer  creek 
to  the  middle  fork'  of  the  American  River.  There  are  now  known 
only  two  main  groves,  and  while  in  all  there  are  several  thousand 
sizable  trees,  the  number  of  trees  remarkable  for  their  size  does 


540 


RELATION  TO   ENVIRONMENT. 


Fig.  499. 
The  Big  tree,  Sequoia  washingtoniana.     (Bureau  Forestry,  U.  S.  Dept.  Agr.) 


FOREST  SOCIETIES.  541 

not  exceed  500.  The  trees  range  in  height  from  250  to  360 
feet,  and  the  larger  ones  from  20  to  35  feet  in  diameter,  while 
the  bark  of  the  larger  trees  is  2  feet  thick.  They  occur  at  an 
elevation  of  4500  to  7000  feet.  They  do  not  occur  alone,  but 
the  other  principal  trees  of  the  forest  mixed  with  them  are  the 
pitch-pine,  sugar-pine,  Douglas  spruce,  white  fir,  and  bastard 
cedar. 

1022.  Geological  history  of  the  Big  tree.— Evideri^  of  fossil 
specimens  collected  in  Alaska,  British  America,  Iceland,  Green- 
land,  Spitzbergen,  Europe,  and  the  Rocky   Mountains   in   the 
United  States  shows  that  several  species  of  the  Sequoia  existed  in 
the  Miocene  period,  and  one  of  these,  the  Big  tree,  must  have 
grown  in  Greenland  as  well  as  in  the  lower  latitude  of  Europe. 
During  glacial  times  they  were  destroyed  in  Europe,  probably 
because  in  their  southward  migration  they  could  not  pass  the 
barrier  of  transcontinental  mountain  chains  in  southern  Europe, 
while  they  were  permitted  in  North  America  to  migrate  south 
of  the  extent  of  the  cold  wave  and  thus  were  saved  from  extinc- 
tion. 

1023.  Preservation  of  the  Big  trees.— The  greater  part  of  the 
Big  trees  are  owned  by  private  interests  or  by  lumbering  com- 
panies, but  the  U.  S.  government  owns  and  controls  in  large  part 
two  large  areas  within  the  Sequoia  and  General  Grant  National 
Park,  while  the  State  of  California  owns  one  tract,  the  Mariposa 
Grove,  an  area  of  about  two  miles  square,  which  is  held  as  a  State 
park. 

IV.  Tropical  Forests. 

1024.  Kinds  of  tropical  woods. — According  to  Schimper  the 
woods  in  the  tropics  are  divided  into  three  groups:  ist.  The  ever- 
green forest,  which  occurs  in  the  areas  of  great  rainfall  where  there 
is  no  dry  period.     The  woods  are  hygrophile  in  character,  are 
at  least  30  meters  high,  and  usually  much  higher.     Besides  the 
forest  trees  there  are  numerous  stout  lianas,  i.e.,  climbing  trees 
and  vines  as  well  as  woody  and  herbaceous  epiphytes.      2d.  Mon- 


542  RELATION    TO   ENVIRONMENT. 

sun  woods  occur  in  those  regions  of  considerable  rainfall,  but 
with  a  dry  period,  during  the  latter  part  of  which  the  trees  are 
bare  of  leaves.  The  woods,  therefore,  are  markedly  of  a  tropo- 
phile  character,  resembling  in  this  respect  the  deciduous  trees 
which  lose  their  leaves  during  the  winter  period.  The  trees  are 
less  in  height  than  those  of  the  evergreen  forest,  are  rich  in  woody 
lianas  and  in  herbaceous  epiphytes,  but  poor  in  woody  epiphytes. 
3d.  The  savanna  woods  and  the  thorn  woods.  These  are  rarely 
evergreen  during  the  dry  period.  The  savanna  woods  are  about 
20  meters  high,  are  poor  in  undershrubs,  lianas,  and  epiphytes, 
but  rich  in  grasses  and  other  herbs  growing  on  the  ground.  The 
thorn  woods  as  well  as  the  savanna  woods  are  xerophile  in  char- 
acter, very  rich  in  undershrubs  and  slender-stemmed  lianas,  are 
poor  in  herbs  and  grasses,  and  mostly  without  epiphytes. 

1025.  The  evergreen  tropical  forests. — These  are  remarkable 
for  the  great  number  of  species  and  of  individuals,  and  for  the 
great  mass  of  vegetation.  There  is  usually  such  a  dense  growth  of 
tall  forest  trees  that  the  light  is  shut  out  from  the  forest  floor  and 
interior  to  such  an  extent  as  to  largely  prevent  the  growth  of 
smaller  vegetation  upon  the  forest  floor.  The  forest  is  therefore 
noted  for  its  epiphytes,  herbaceous  as  well  as  woody,  which  grow 
in  great  numbers  upon  the  branches,  within  or  just  beneath 
the  forest  canopy,  where  they  are  better  situated  in  reference 
to  light.  It  is  interesting  to  note  that  in  the  reforestation  of 
the  volcanic  areas  in  west  Java,  for  example,  a  number  of  these 
epiphytes  are  found  growing  on  the  bare  lava,  among  ferns  and 
other  low  vegetation.  Here  they  have  a  suitable  relation  to 
light,  but  when  the  forest  finally  develops  in  such  regions,  as  it 
will  if  undisturbed,  these  epiphyte  species  now  growing  on  the 
ground  will  migrate  to  the  forest  canopy.  The  evergreen  broad - 
leaved  forests  are  largely  within  the  tropics,  though  there  is  some 
extension  into  parts  of  the  south  temperate  region.  While  the 
forest  represents  the  climax  type  of  vegetation,  the  evergreen 
forest  of  the  tropics  is  the  climax  type  of  forest  formation.  The 
evergreen  tropical  forests  are  found  in  those  tropical  areas  where 
the  rainfall  is  very  great  and  is  also  evenly  distributed  throughout 


FOREST  SOCIETIES.  543 

the  year,  so  that  soil  moisture  and  atmospheric  humidity,  while 
showing  some  variations,  are  relatively  high  throughout  all  seasons. 
This  with  the  high  degree  of  heat  maintained  throughout  the 
year  provides  most  favorable  conditions  for  rapid  and  continued 
growth. 

1026.  Absence  of  climatic  periodicity  in  evergreen  tropical 
forests. — The  absence  of  climatic  periodicity  in  these  ever-damp 
tropical  areas  is  most  striking  in  its  effect  on  the  general  charac- 
ter of  the  vegetation  as  compared  with  those  tropical  areas  where 
climatic  periodicity  is  present,  i.e.,  a  dry  season  extending  over 
a  considerable  period  and  alternating  with  a  rainy  season,  as 
well  as  the  climatic  periodicity  in  the  temperate  regions,  where  a 
cold  season  alternates  with  the  warm  growing  season.  The 
more  striking  effects  are,  ist,  almost  continual  growth;  2d,  the 
absence  of  bud-scales  on  the  buds,  since  there  is  no  austere  season 
when  these  are  needed  to  protect  the  young  growing  part,  as  is 
the  case  in  the  dry  tropical  or  subtropical  areas,  or  during  the 
cold  season  in  temperate  and  arctic  regions;  3d,  absence  of  uni- 
formity in  the  time  of  defoliation :  since  there  are  no  climatic  changes 
which  necessitate  uniformity,  a  tree  sheds  its  leaves  and  in  a  few 
days  puts  out  a  new  crop;  4th,  an  extended  flowering  and  fruiting 
period  for  many  species,  so  that  flowering  and  fruit-bearing  often 
overlap  in  the  same  tree,  though  this  does  not  continue  through- 
out the  year;  5th,  a  very  dense  forest  canopy  because  of  the 
favorable  conditions  of  growth  and  the  large  size  and  number  of  the 
leaves  making  the  interior  of  the  forest  darker  than  in  any  other 
forest  areas,  thus  lessening  the  proportion  of  herbage  on  the  forest 
floor-,  6th,  there  is  a  relatively  small  amount  of  humus,  the  high 
degree  of  heat  and  moisture  favoring  rapid  decay  of  fallen  leaves 
and  wood;  yth,  in  the  many  structures  for  protection  of  leaves 
against  excessive  wetting  and  the  beating  of  heavy  rains;  a 
thick  cuticle  and  often  hairy  leaves  are  examples  of  adaptations, 
while  some  interesting  cases  are  known  where  the  upper  side  of  the 
leaves  is  furrowed  along  the  line  of  the  veins,  these  uniting  and 
converging  on  the  margin  into  a  " gutter"  which  terminates  on 
the  external  midrib  at  the  leaf  tip,  forming  a  drainage  system  for 


544  RELATION    TO   ENVIRONMENT. 

the  leaf  surface.  Then  the  leaves  of  most  tropical  plants  are 
thick  and  firm,  as  in  the  rubber  plant,  banana,  orchids,  bromelias, 
tillandsias,  palms,  etc.,  which  afford  them  protection  against  the 
beating  action  of  heavy  and  prolonged  rains.  8th,  against  exces- 
sive heat  and  insulation,  leaves  of  trees  are  protected  by  a  vertical 
position  of  the  highest  ones,  while  those  lower  in  the  canopy  are 
horizontal. 

1027.  Competition  in  evergreen  tropical  forests. — Thus  cli- 
mate is  largely  eliminated  as  a  factor  in  the  plant's  struggle  for 
existence.     Plants  are  left  to  compete  among  themselves  for  space 
on  the  ground,  space  in  the  air,  and  for  light.     This  competition 
has  reached  its  highest  pressure  in  the  evergreen  tropical  forest. 
In  all  forest  societies  trees  have  outdistanced  their  rivals  in  the 
struggle  for  space  and  light.     This  is  because  of  their  height, 
by  means  of  which  they  are  enabled  to  reach  above  and  beyond 
other  plants.     They  overcome  their  rivals  by  casting  a  shade 
over  them  in  which  they  cannot  grow,  or  at  least  only  preserve  a 
miserable  existence.     Only  plants  tolerant  of  shade   can   grow 
beneath  the  forest  canopy,  and  these  rarely  become  successful 
rivals  of  the  trees.     The  most  dangerous  competitors  of  trees 
under   such    circumstances    are    parasites    and   epiphytes    and 
lianas. 

1028.  Epiphytes  in  the  evergreen  tropical  forest. — In  all  for- 
est societies  epiphytes  are  present,  but  they  have  reached  their 
climax  in  size,  numbers,  and  effective  rivalry  with  forest  trees, 
in  the  evergreen  tropical  forest.     The  darkness  cf  the  interior  of 
the   forest   largely   prevents   the   development   of   even   tolerant 
shade  plants  on  the  forest  floor.     Undershrubs  and  herbs  have, 
as  a  consequence,  migrated  from  the  forest  floor  to  the  forest 
canopy,  where  they  are  crowded  in  surprising  masses  in  tier  after 
tier  upon  the  trunks  and  branches,  even  to  the  upper  extremity  of 
the  same;  while  on  the  uppermost  leaves  mosses,  algae,  and  lichens 
abound,   as  well  as   on   the  leaves  and  branches  lower  down. 
Numerous  orchids,  ferns,  bromelias,  tillandsias,  and  shrubs  load 
the  trees  down  in  some  cases  with  such  a  weight  that  the  branches 
or  tree  are  broken  down.     Where  there  are  open  places  in  the 


FOREST  SOCIETIES. 


545 


stand  of  trees  the  admitted  light  encourages  a  luxuriant  growth 
down  the  interior  and  even  on  the  forest  floor. 

1029.  Lianas  in  the  evergreen  tropical  forest.— Lianas  are 
climbing  vines  or  trees.  Lianas  occur  in  forests  of  temperate 
regions,  but  they  attain  their  highest  development  in  the  tropics. 


Fig.  500. 
A  liana  in  the  Botanic  Garden  at  Peradenyia.     (After  Schimper.) 

In  size  they  vary  from  the  more  slender  serpent-like  twining  stems 
to  immense  trunks,  coiled  on  the  ground  and  around  the  boles 
of  forest  trees,  where  they  branch  and  ascend  in  tangled  masses 
into  the  forest  canopy. 


54-6  RELATION   TO   ENVIRONMENT. 

1030.  Value  of  tropical  forests. — The  forests  of  the  tropics  are 
of  vast  extent,  and  fully  one  half  of  the  area  covered  by  them  has 
hardly  been  explored.     Many  of  the  woods  are  of  very  great  value 
In  regard  to  the  Amazon  basin,  Agassiz  says,  "Nowhere  in  th* 
world  is  there  finer  timber,  either  for  solid  construction  or  for 
works  of  ornament."     A  number  of  things  have  stood  in  the  way 
of  the  exploitation  of  the  tropical  forests,  chief  among  them  being 
the  climate  and  the  great  luxuriance  of  the  forest  itself;  it  is  very 
likely  that  in  the  future  the  work  of  exploiting  the  forests  of  the 
tropics  will  be  greatly   developed.     Many  useful   products  are 
derived  from  a  large  number  of  different  kinds  of  tropical  trees. 
(See  Gifford,  Practical  Forestry.) 

V.  Relation  of  Forests  to  Rainfall. 

1031.  Forests  do  not  materially  increase  rainfall  of  a  region. 

— In  a  study  of  the  climatic  vegetation  regions  it  is  clear  that  the 
forest  is  dependent  on  rainfall,  anti  below  a  certain  minimum 
annual  precipitation,  not  very  definitely  determined,  forests  will 
not  develop,  and  of  course  the  rainfall  must  be  rather  evenly 
distributed  throughout  the  year,  or  at  least  through  the  growing 
season.  But  that  the  rainfall  of  a  region  is  influenced  by  the 
forest  to  any  great  extent,  as  is  often  supposed,  is  not  so  evident. 
Long-continued  droughts  during  the  growing  season  which  occur 
now  and  then,  and  the  great  accompanying  forest  fires,  show 
the  inability  of  the  forest  to  produce  rainfall  per  se.  Rainfall  is 
due  to  moisture-laden  air-currents  from  warm  bodies  of  water 
coming  in  contact  with  the  cooler  air  of  coast  lines,  mountain 
chains,  or  cooler  air-currents  from  colder  regions.  The  movement 
of  these  air-currents  is  controlled  by  barometric  pressures,  a  storm 
center  originating  in  an  area  of  low  barometric  pressure  and 
moving  to  one  of  high  pressure.  But  forests  do  account  to  some 
extent  for  a  certain  per  cent  of  the  rainfall  of  the  region.  The 
forest  floor  holds  back  a  large  amount  of  the  precipitation  of 
moisture-laden  air  coming  from  a  distance.  Through  trans- 
piration the  forest  leaves  as  well  as  those  of  other  vegetation, 
together  with  evaporation  from  the  forest  floor  and  streams,  load 


FOREST  SOCIETIES.  547 

the  air  with  vapor.  In  mountainous  countries  where  we  can 
obtain  a  bird's-eye  view  of  large  forest  areas,  it  is  a  common  and 
interesting  sight  to  see  the  cloud  formation.  Here  and  there,  as 
the  invisible  water-vapor  rises  and  comes  in  contact  with  the 
cooler  air,  one  can  see  forming  clouds  of  white  mist  in  the  morn- 
ing which  grow  in  size  as  they  rise,  unite  with  others,  become 
more  dense  and  center  around  and  obscure  some  large  mountain 
peak  as  they  change  into  black  "thunder-clouds,"  then  move  and 
precipitate  their  moisture  over  valley  and  mountain  in  the  after- 
noon. Even  when  the  air  is  not  cool  enough  to  cause  precipita- 
tion of  the  moisture,  the  mist  coming  in  contact  with  the  cool 
surfaces  of  leaves,  twigs,  and  branches  condenses  into  water 
which  drips  from  their  surface. 

1032.  Importance  of  the  forest  in  the  disposal  of  rainfall. 
The  importance  of  the  forest  in  disposing  of  the  rainfall  is  very 
great.     The  great  accumulation  of  humus  on  the  forest  floor 
holds  back  the  water  both  by  absorption  and  by  checking  its  flow 
so  that  it  does  not  immediately  flow  quickly  off  the  slopes  into  the 
drainage  system  of  the  valley.     It  percolates  into  the  soil.     Much 
of  it  is  held  in  the  humus  and  soil.     What  is  not  retained  thus 
filters  slowly  through  the  soil  and  is  doled  out  more  gradually 
into  the  valley  streams  and  mountain  tributaries,  so  that  the 
iood  period  is  extended,  and  its  injury  lessened  or  entirely  pre- 
vented, because  the  body  of  water  moving  at  any  one  time  is 
not  dangerously  high.     The  winter  snow  is  shaded  and  in  the 
spring  melts  slowly,  and  the  spring  freshets  are  thus  lessened. 
The  action  of  the  leaves  and  humus  in  retarding  the  flow  of  the 
water  prevents  the  washing  away  of  the  soil;   the  roots  of  trees 
bind  the  soil  also  and  assist  in  holding  it. 

1033.  Absence  of  forest  encourages  serious  floods. — The  great 
floods  of  the  Mississippi  and  its  tributaries  are  due  to  the  rapid- 
ity with  which  heavy  rainfall  flows  from  the  rolling  prairies  of 
the  west,  and  from  the  deforested  areas  west  of  the  Alleghany 
system.     The  serious  floods  in  recent  years  in  some  of  the  South 
Atlantic  States  are  in  part  due  to  the  increasing  area  of  deforesta- 
tion in  the  Blue  Ridge  and  Southern  Alleghany  system.     The 


548  RELATION   TO   ENVIRONMENT. 

effect  of  floods  from  heavy  rains  there  is  evident  to  one  who 
drives  for  50  to  100  miles  through  the  mountains,  where  valley 
roads  become  torrential  streams,  harvested  crops  of  wheat  and 
oats  and  hay  are  swept  into  the  rivers,  while  dwelling-houses 
and  even  the  surface  soil  are  not  exempt  from  the  same  fate. 
On  mountain  slopes  where  the  soil  is  thin,  it  is  sometimes  swept 
clean  to  the  bare  rock  after  deforestation.  The  suddenness 
with  which  the  water  now  rushes  down  the  mountain  slopes 
from  numerous  rivulets  and  branches,  and  unites  in  the  rivers, 
sometimes  forms  a  huge  wave  of  water  20  to  30  feet  at  its  crest 
which  rolls  on  across  the  coastal  plains  to  the  ocean,  often  carry- 
ing destruction  to  life  and  property  along  its  course.  To  one 
who  has  not  been  in  the  Blue  Ridge  Mountains  a  good  picture 
of  the  devastating  work  of  floods  following  the  partial  deforesta- 
tion of  these  mountains  can  be  gained  by  consulting  the  Message 
of  President  Roosevelt  to  Congress,  recommending  the  estab- 
lishment of  a  southern  Appalachian  Forest  Preserve.  The 
aggregate  damage  from  floods  along  the  southern  Appalachian 
streams  in  the  year  1901-02,  reached  the  sum  of  $18,000,000. 

VI.  Forest  Regeneration  and  Protection. 

1034.  Regeneration  of  forests. — If  the  forest  is  to  be  per- 
petuated there  must  be  regeneration,  or  in  time  all  the  trees  will 
die  and  the  forest  thus  become  extinct.  Natural  regeneration 
takes  place  in  two  ways:  ist,  through  the  seed;  and  2d,  by 
the  growth  of  sprouts  from  the  stump  when  the  tree  is  cut,  or 
from  the  roots.  These  sprouts  are  called  coppice.  Trees  which 
are  shade-endurers  are.  apt  to  have  the  advantage  in  the  natural 
regeneration  of  the  forest.  The  hemlock  spruce,  for  example, 
is  a  shade-endurer,  and  thus  the  seedlings  and  young  trees  in  the 
forest  stand  a  good  chance  of  coming  to  maturity^  The  red- 
wood (Sequoia  sempervirens)  is  a  light-demander  and  so  natural 
regeneration  by  seed  is  difficult  except  in  open  places.  The 
redwood,  however,  develops  abundant  coppice,  and  the  great 
amount  of  nutriment  in  the  roots  of  the  large  trees  supplies  it 


FOREST  SOCIETIES.  549 

with  an  abundance  of  food,  so  that  it  grows  rapidly,  the  stems 
often  becoming  quite  tall,  and  the  young  trees  remaining  white 
except  for  a  small  crown  of  green  leafage  at  the  top.  The  Big 
tree  (S.  washingtoniana)  regenerates  by  seed,  and  while  not  a 


Fig.  501. 

Abandoned  field,  Alabama,  self -reforested  by  pines.  (Photograph  by  Prof. 
P.  H.  Mell.)  A  Coniferous  Forest  Society. 

great  shade-endurer,  enough  seedlings  survive  to  provide  a  suc- 
cession of  different  ages  where  lumbering  is  not  practiced. 

Very  few  of  the  other  conifers  can  develop  effective  coppice. 
They  are  dependent  on  the  seed  for  natural  regeneration.  On 
the  other  hand  broad-leaved  trees  develop  abundant  coppice, 
and  in  this  respect  have  the  advantage  over  conifers  which  are 


550 


RELATION   TO   ENVIRONMENT. 


not  shade-endurers  or  do  not  develop  coppice.      Broad-leaved 
trees  are  limited,  however,  in  their  competition  with  conifers  on 


Fig.  502. 

Coppice  from  redwood  showing  sprouts  6  to   8  years  old. 
Bureau  of  Forestry.) 


(From  Bull.   38, 


thin  sandy  soil,  and  in  cold  regions,  because  many  species  of  the 
latter  can  grow  with  a  lower  sum  total  of  heat. 

1035.  Artificial  regeneration  of  forests. — This  is  accomplished 
by  the  aid  of  man,  and  is  one  of  the  lines  of  forestry  work  which 
we  call  silviculture.  This  work  may  vary  in  intensity  all  the 
way  from  leaving  a  few  seed-trees  in  the  forest  here  and  there, 
when  cutting  out  the  merchantable  timber  for  self-seeding,  to 
the  complete  reforestation  of  completely  deforested  areas.  The 
extent  to  which  artificial  regeneration  of  forests  can  be  success- 
fully undertaken  from  a  business  standpoint  will  depend  upon 
the  condition  of  the  forest,  the  price  of  lumber,  expense  of  oper- 


FOREST  SOCIETIES.  55 1 

ation,  and  cost  of  marketing.  It  is  the  province  of  forestry  tc 
educate  for,  as  well  as  to  practice  the  principles  of,  economic 
harvesting  and  cultivation  of  forest  crops,  as  well  as  the  encour- 
agement of  forest  protection  and  planting  where  necessary  for 
the  welfare  of  the  race. 

1036.  Systems  of  management  in  cutting  and  regeneration 
of  forests. — Several  systems  of  forest  management  have  been  de- 
veloped which  are  expressed  briefly  by  Gifford  as  follows: 

I.  "The    selection    system,    which    is    especially    adapted    to 
uneven-aged  or  irregular  protection  forests. 

II.  "  The  system  of  clear-cutting  and  then  regenerating  by 
planting  with  young  trees,  or  by  sowing  the  seed,  or  by  waiting 
until  the  wind  sows  it  from  an  adjoining  forest. 

III.  "The  system  of  regenerating  pure  forests  naturally  by 
uniformly   and   gradually   thinning   throughout,    and   admitting 
light  in  such  a  way  that  the  seeds  will  germinate  and  the  young 
growth  properly  develop. 

IV.  "  The  coppice  system,  where  the  forest  consists  of  species 
which  will  sprout  from  the  stump  or  the  root." 

1037.  Protection  of  forests.— The  fact  that  forests  have  an 
important  influence  in  regulating  the  movement  and  disposal  of 
rainfall   has   led   the   National   Government   and   several   State 
Governments  to  adopt  forest  policies   and   to   set   apart  certain 
forest  areas,  especially  in  mountainous  districts,  as  reservations, 
where  lumbering  is  prohibited  by  law  and  efforts  made  to  regen- 
erate the  forests  where  necessary  and  protect  them  from  fire. 
The  value  of  these  forest  reservations  is,  ist,  the  protection  of 
game  and  other  wild  animals;    2d,   holding  in  reserve  water- 
storage  for  power,  as  well  as  for  city  supplies;   3d,  the  protection 
of  the  valleys  and  lowlands  from  destructive  floods;    4th,  the 
providing  healthful  resorts  where  people  find  rest  from  the  busy 
and  exacting  professional  and  business  lives.     When  the  prin- 
ciples of  forestry  are  better  understood  by  the  people  the  reser- 
vations will  probably  be  cropped  and  regenerated  according  to 
some  suitable  system  which  will  not  lessen  their  value  for  the 
purposes  for  which  they  were  first  set  apart,  and  at  the  same 


552  RELATION   TO   ENVIRONMENT. 

time  will  yield  the  state  a  revenue  sufficient  to  more  than  pay 
for  the  cost  of  management,  and  also  will  tend  to  keep  within 
reasonable  bounds  the  price  of  building  materials. 

1038.  Forest  planting  in  unforested  areas. — Successful  at- 
tempts have  been  made  to  grow  forests  in  the  prairie  regions  of 
the  West  (the  "plains"  east  of  the  icoth  meridian)  by  trans- 
planting seedlings  and  cultivating  them  and  protecting  them  until 
they  are  large  enough  to  shade  the  ground  and  hold  their  litter. 
These  forests  provide  their  owner  shelter  for  orchards,  provide 
fire-wood,  fence-posts,  and  some  lumber  for  building  material. 
In  Gascony  (France)  an  arid,  sandy  area  was  planted  with  pines 
to  hold  the  sand.     The  swamp  regions  here  were  also  reclaimed 
by  planting  forests.     What  was  once  an  unhealthful  area  is  now 
a  health-resort.      Certain  species  of  eucalyptus  which  grow  in 
wet  ground  have  been  planted  in  swampy  lands  to  drain  them. 
This  tree  requires  a  great  amount  of  water  and  transpires  large 
amounts. 

1039.  Enemies    of   the    forest.— Outside  of  the  destructive 
injury  of  fires,  wind,  or  the  careless  operations  of  man,  as  well 
as  climatic  and  soil  factors  which  are  inimical  to  forest  develop- 
ment, mention  should  be  made  of  biotic  factors.     Many  forms  of 
life  interfere  with  the  perfect  development  of  trees  or  act  as  de- 
structive agents.     Insects  feed  upon  and  destroy  leaves,  branches, 
and  trunks;    herbivorous  animals  feed  upon  foliage,  buds,  and 
twigs.     We   are   concerned   here   chiefly,    however,    with   plant 
enemies.     These  are  parasites  and  wood-destroying  fungi.     The 
most  important  parasites  are  among  the  fungi,   though   some 
seed  plants,  like  the  mistletoe,  " beech  drops,"  "pine  sap,"  arceu- 
thobium,   etc.,   do  slight  injury  to  some  trees.     The  parasitic 
fungi  injurious  to  trees  are  found  among  the  rusts,  mildews, 
molds,  and  a  few  among  the  mushrooms,  black  fungi,  and  cup 
fungi.     The    fungi,    however,    which    are    more    destructive    to 
timber  trees  are  chiefly  found  among  the  mushrooms  and  their 
near   relatives.     They  are   known   as  "wound"    parasites   and 
wood-destroying  fungi.     It  is  quite  easy  in  many  cases  for  one 
possessing  no  technical  knowledge  of  the  subject  to  read  the 


FOREST  SOCIETIES 


553 


Fig.  503. 
Wood-destroying  fungus  (Hydnum  septentrionale)  on  living  maple,  reduced 

(Phot.oprq/nh   hv  the   author  J 


554 


RELATION    TO   ENVIRONMENT. 


Fig.  504- 

Spawn  of  the  "mushroom"  as  it   makes 
its  way  through  the  wood  of  the  tree. 


story   of    these    "  wood-destroying "    fungi    in    the    living   tree. 

Branches  broken  by  snow, 
by  wind,  by  falling  timber, 
provide  entrance  areas  where 
the  spores,  lodging  on  the 
heart-wood  of  broken  timber, 
or  on  a  bruise  on  the  side 
of  the  trunk,  which  has 
broken  through  the  living 
part  of  the  tree  lying  just 
beneath  the  bark,  provide 
a  point  for  entrance.  The 
living  substance  (protoplasm) 
in  the  spawn  exudes  a 
"juice"  (enzyme)  which  dis- 
solves an  opening  in  the  wood  cells  and  permits  the  spawn  to 
enter  the  heart  of  the  tree,  where  decay  rapidly  proceeds  as  a 
result.  But  very  few  of  these  plants  can  enter  the  tree  when 
the  living  part  underneath  the  bark  is  unbroken. 

These  observations  suggest  useful  topics  for  thought.  They 
suggest  practical  methods  of  prevention,  careful  forestry  treat- 
ment, and  careful  lumbering  to  protect  the  young  growth  when 
timber  trees  are  felled.  They  suggest  careful  pruning  of  fruit 
and  shade  trees,  by  cutting  limbs  smooth  and  close  to  the  trunk, 
and  then  painting  the  smooth  surface  with  some  lead  paint. 

1040.  Scavenger  members  of  the  forest  societies. —  While 
many  of  the  mushrooms  are  enemies  of  the  forest,  "they  are,  at 
the  same  time,  of  incalculable  use  to  the  forest.  The  mushrooms 
are  nature's  most  active  agents  in  the  disposal  of  the  forest's 
waste  material.  Forests  that  have  developed  without  the  guid- 
ance of  man  have  been  absolutely  dependent  upon  them  for 
their  continual  existence.  Where  the  species  of  mushrooms  are 
comparatively  few  which  attack  living  trees,  there  are  hundreds 
of  kinds  ready  to  strike  into  fallen  timber.  There  is  a  degree  of 
moisture  present  on  the  forest  floor  exactly  suited  to  the  rapid 
growth  of  the  mycelium  of  numbers  of  species  in  the  bark,  sap- 


FOREST  SOCIETIES.  555 

wood,  and  heart- wood  of  the  fallen  trees  or  shrubs.  In  a  few 
years  the  branches  begin  to  crumble  because  of  the  disorganiz- 
ing effect  of  the  mycelium  in  the  wood.  Other  species  adapted 
to  growing  in  rotting  wood  follow  and  bring  about,  in  a  few  years, 
the  complete  disintegration  of  the  wood.  It  gradually  passes 
into  the  soil  of  the  forest  floor,  and  is  made  available  food  for 
the  living  trees.  How  often  one  notices  that  seedling  trees  and 
shrubs  start  more  abundantly  on  rotting  logs. 

"The  fallen  leaves,  too,  are  seized  upon  by  the  mycelium  of  a 
great  variety  of  mushrooms.  It  is  through  the  action  of  the 
mycelium  of  mushrooms  of  every  kind  that  the  fallen  forest 
leaves,  as  well  as  the  trunks  and  branches,  are  converted  into 
food  for  the  living  trees.  The  fungi  are,  therefore,  one  of  the 
most  important  agents  in  providing  available  food  for  the  virgin 
forest. 

"The  mushrooms  also  prevent  the  forest  from  becoming 
choked  or  strangled  by  its  own  fallen  timber.  Were  it  not  for 
the  action  of  the  mushroom  mycelium  in  causing  the  decay  of 
fallen  timber  in  the  forest,  in  time  it  would  be  piled  so  high  as 
to  allow  only  a  miserable  existence  to  a  few  choked  individuals 
The  action  of  the  mushrooms  in  thus  disposing  of  the  fallen 
timber  in  the  forests,  and  in  converting  dead  trees  and  fallen  leaves 
into  available  food  for  the  living  ones,  is  probably  the  most  impor- 
tant role  in  the  existence  of  these  plants.  Mushrooms,  then,  are 
to  be  given  very  high  rank  among  the  natural  agencies  which 
have  contributed  to  the  good  of  the  world.  When  we  con- 
template the  vast  areas  of  forest  in  the  world  we  can  gain  some 
idea  of  the  stupendous  work  performed  by  the  mushrooms  in 
4'housecleaning?  and  in  'preparing  food,'  work  in  which  they 
are  still  engaged."  (Atkinson,  in  Mushrooms,  Edible,  Poison- 
ous, etc.) 


CHAPTER  LI. 

THE    PRAIRIE   AND    PLAINS   SOCIETIES. 

I.  Grass-land  Formations. 

1041.  Types  of  the  grass-land. — Grass-land  formations  are  of 
three  general  types:    ist,  Savannas;  2d,  Prairies  or  Meadows; 
3d,  Plains  or  Steppes. 

1.  Savannas. — This  term  is  applied  to  the  grass-land  forma- 
tions in  warm  temperate  or  subtropical  countries  where  scattered 
trees  or  tree-clumps  occur.     The  regions  are  too  dry  at  certain 
seasons  for  the  development  of  a  woodland  formation  and  yet 
not  dry  enough  for  the  desert  type.     So  grasses  make  the  charac- 
teristic climatic  formation.     But  there  is  sufficient  moisture  and 
absence  of  high  winds  to  permit  the  development  of  numbers  of 
trees. 

2.  Prairie. — The  prairies  (or  meadows  according  to  Schimper) 
are  grass  formations  in  the  cold  temperate  regions  where  there 
is  sufficient  moisture  to  induce  a  close  formation.     They  differ 
from  savannas  in  the  absence  of   trees.     The  high  winds  and 
very  dry  summer  season  prevent  the  development  of  trees. 

3.  Plains  (or  Steppes).     The  plains  or  steppes  are  grass-land 
formations  principally,  but  usually  the  formation  is  more  open 
because  of  the  greater  aridity  of  the  climate.    See  paragraph  below 
on  extent  of  prairie  and  plains  in  the  United  States. 

1042.  Extent  of  prairie  and  plains  region  in  United  States. 
—The  prairie  vegetation  region  in  North  America  extends  over 
the  arid  areas  of  the  austral  region  east  of  the  Rocky  Mountains, 

556 


VEGETATION  OF   THE   PRAIRIE.  557 

extending  into  western  Texas  and  Kansas  in  the  south,  and 
northward  extending  as  far  east  as  western  Illinois.  The  area  east 
of  the  Missouri  River  has  a  greater  annual  rainfall,  and  here  is  the 
typical  prairie  vegetation,  which  is  of  the  meadow  type.  Passing 
westward  and  southward  the  region  of  the  "  Great  Plains,"  or 
the  arid  region,  is  entered,  where  the  rainfall  is  less  and  the  vege- 
tation is  that  of  the  steppes;  while  toward  the  foot  of  the  Rocky 
Mountains  southward  the  dryness  of  the  region  increases  ari 
partakes  more  of  the  character  of  the  desert.  The  typical  prairie 
region  of  North  America  extends  from  about  the  looth  meridian 
eastward  to  the  forests  of  Illinois  and  Indiana,  including  most 
of  the  Dakotas,  Nebraska,  Iowa,  southern  Minnesota,  and  Wis- 
consin, a  large  part  of  Kansas  and  Indian  Territory,  and  extends 
north  into  western  Manitoba  and  nearly  all  of  Assiniboia  and 
Saskatchewan.  The  surface  of  the  ground  is  rolling  and  fur- 
rowed, the  prairie  grass  formation  on  the  rolling  elevations, 
with  the  so-called  "gallery  woods"  or  " park-like"  forest  societies 
at  the  lower  elevations  along  the  streams.  This  is  the  transition 
area  from  the  forest  area  to  the  arid  regions,  or  steppes. 

II.  Prairie  Formations. 

1043.  Tension  line  between  forest  and  prairie. — The  tension 
line  between  the  forest  region  and  the  prairie  region  was  long 
since  established.     This  line  of  separation  is  not  well  marked, 
for  there  is  not  an  abrupt  transition  from  forest  to  prairie.     Arms 
of  the  prairie  are  outstretched  now  and  then  between  extended 
troops  of  forests,  and  clumps  of  shrubbery  and  trees  for  some 
distance  further  dot  the  prairie  here  and  there  like  sentries  guard- 
ing the  outposts  of  the  main  division. 

1044.  Climatic  factors  the  dominant  ones  in  limiting  forest 
and  prairie  areas.— While  the  general  climatic  influences  have 
been  the  chief  factors  in  delimiting  these  regions,  biotic  or  physi- 
cal factors  may  in  some  cases  have  aided.     For  example,  it  has 
been  suggested  that  the  bison  grazing  on  the  prairies  in  central 
United  States  may  have  aided  in  preventing  trees  and  shrubs 


558 


RELATION   TO  ENVIRONMENT. 


from  getting  a  start.  Also  prairie  fires  may  have  destroyed 
them  in  the  seedling  stage.  But  it  is  quite  clear  that  climatic 
factors  have  been  the  dominant  ones.  ist.  The  greater  amount 
of  rainfall  is  in  the  spring  and  early  summer,  when  the  grasses  of 


Fig.  505- 

Typical  prairie  scene,  a  few  miles  west  of  Lincoln,  Nebraska.     (Bot.  Dept.,  Univ. 
Nebraska.) 

the  prairie  most  need  it.  2d.  This  is  the  time  when  seeds  of 
trees  would  germinate.  Those  enabled  to  start  would  die  out 
during  the  drought  of  late  summer  and  autumn.  3d.  The  firm- 
ness of  the  soil  and  dense  mat  of  grasses  would  largely  prevent 
seedlings  getting  a  foothold  in  the  ground.  4th.  The  heavy  and 
drying  winds  during  the  dry  season  and  winter  cause  excessive 
transpiration,  and  scatter  the  litter,  thus  preventing  the  accumula- 
tion of  humus  which  is  so  necessary  for  the  retention  of  moisture. 
1045.  Prevailing  grasses  in  the  prairie  region. — Among  the 
prevailing  grasses  in  the  prairie  region  are  two  types:  ist,  the 
"sod-formers,"  long-stemmed  grasses  which  make  close  forma- 
tions, as  the  drop-seed  (Sporobolus  asperifolius),  Koehleria 


VEGETATION   OF   THE   PRAIRIE.  559 

cristata,  Eatonia  obtusata,  Panicum  scribnerianum ;  2d,  the 
"  bunch  "-grasses,  like  buffalo-grass  (Bulbilis  dactyloides),  beard- 
grasses  or  broom-sedge  (Andropogon  furcatus  and  scoparius), 
grama-grass  (Bouteloua  oligostachya),  etc.  These  two  types  are 
more  or  less  intermixed,  but  the  "sod-formers"  (  =  " prairie-grass 
formation")  are  especially  characteristic  of  the  lower  prairie 
areas,  while  the  bunch-grasses  (  =  " buffalo-grass  formation")  are 
especially  characteristic  grasses  of  the  arid  region  or  steppes 
farther  west  and  southwest.  They  make  a  close  formation,  but 
in  the  drier  regions  tend  more  and  more  to  an  open  formation 
(see  paragraph  1049). 

III.  The  Plains  Formations. 

1046.  The  Great  Plains  of  the  United  States.— The  Great 

Plains,  as  the  arid-  region  of  the  United  States  is  sometimes 
called,  extend  from  about  the  rooth  meridian  to  the  eastern  foot- 
hills of  the  Rocky  Mountains,  and  they  form  a  transition  area 
from  the  prairie  or  meadow  region  to  the  desert  area  between  the 
Sierra  Nevada  and  western  slope  of  the  Rockies,  the  dryness  of 
the  area  increasing  in  intensity  toward  the  southwest.  The 
prevailing  grasses  in  this  arid  area  are  the  bunch-grasses  (buffalo- 
grass,  beard-grass,  Indian  grass,  etc.),  which  in  the  typical  prairie 
usually  grow  in  close  formation,  but  here,  while  often  forming 
meadow-like  expanses,  grow  in  more  open  formation.  The  other 
prevailing  characteristic  plants  are  the  sage-brush  (Artemisia 
tridentata),  low,  compact,  tufted  shrubs,  grayish  in  color.  The 
prickly-pear  cactus  (Opuntia)  is  also  characteristic  of  the  area, 
but  is  subordinate  and  less  common,  though  it  is  the  dominant 
plant  over  extensive  areas.  Reaching  the  Lower  Sonoran  area 
of  the  Great  Plains  there  is  a  gradual  change  of  the  flora  as  the 
climate  becomes  hotter  and  drier  in  western  Texas  and  New 
Mexico,  where  a  semi-desert  area  (see  paragraph  10540)  exists 
and  extends  into  the  high  table-lands  of  Mexico,  characterized 
,by  giant  cacti,  forming  the  so-called  cactus  deserts.  Thus  there 
are  cactus  societies  (or  cactus  formations).  Opuntia  is  common, 


560  RELATION   TO  ENVIRONMENT. 

and  here  also  occur  the  globose  spiny  forms  called  "pin-cush- 
ions," strawberry  cacti,  etc.,  of  the  genus  Cereus,  according  to 
Bray,  numerous  yuccas  (yucca  formations),  agaves,  also  coarse 
succulents,  and  coarse  rough  shrubby  growths,  like  the  mesquite 
(Prosopis  juliflora),  acacias,  shrubby  junipers,  dwarf  oaks,  etc., 
which  take  the  place  largely  of  the  bunch  grasses  and  sage- 
brush of  the  Northern  Plain's  area,  the  shrubs  and  dwarfed 
trees  often  forming  open  or  dense  thickets  known  as  "chap- 
arral." 

IV.  Edaphic  Formations  in  the  Prairie  Region. 

The  edaphic  formations  in  the  prairie  region  may  be  represented 
by  some  of  those  in  the  prairies  and  Great  Plains  of  the  western 
United  States,  as  follows:  the  forest  formations  along  the  river 
courses,  the  meadows,  the  sand-hills,  the  alkali  areas,  and  the 
Bad  Lands  of  Nebraska  and  South  Dakota. 

1047.  The  forest  formations  along  the  courses  of  the  streams 
are  in  some  cases  continuations  of  the  great  forest  formations  of 
the  eastern  United  States,  which  reach  far  up  the  fertile  and 
moist  valleys  of  the  larger  rivers.  In  some  cases  the  forests  are 
more  or  less  interrupted  and  scattered,  where  the  valleys  are  nar- 
row, or  along  smaller  streams  where  they  take  on  the  form  of 
"gallery  woods"  or  "park- like"  formations.  The  relation  to 
the  forest  formations  of  the  east  is  shown  by  the  presence  of 
many  eastern  species,  as  the  black  walnut,  several  species  of  oak, 
hickories,  elms,  paper-birch,  etc.  In  the  lower  moist  valleys 
broad-leaved  deciduous  trees  prevail,  while,  in  the  higher  and 
drier  bluffs,  is  the  xerophytic  coniferous  forest.  While  many 
species  represent  the  invasion  of  elements  from  the  eastern 
forest,  others  represent  the  eastern  extension  of  trees  from  the 
Rocky  Mountain  region  and  the  foot-hills.  For  example,  the 
yellow  pine  (Pinus  scopularum)  in  Nebraska  along  the  Niobrara 
River  meets  and  mingles  with  trees  from  the  eastern  forest  (min- 
gles with  the  black  walnut,  according  to  Bessey),  or  forms  pure 
forests. 


VEGETATION  OF  THE  PRAIRIE^  $6l 

1048.  Meadows. — These  meadow  formations  (see  Pound  & 
Clements)  are  found  usually  along  river  courses  and  around 
lakes,  and  are  intermediate  between  the  forest  formations  and 
the  prairie.  They  are  characterized  by  long-stemmed  grasses 
which  are  "sod-formers"  (Elymus  canadensis,  Stipa  spartea, 


Pig.  5060. 

Belt  of  forest  bordering  a  stream  in  southeastern  Nebraska.     (Bot.  Dept.,  Univ. 
Nebr.) 

Agropyron   pseudorepens,    etc.).      Some    of    the    bunch-grasses 
occur  as  secondary  grasses. 

1049.  The  sand-hills.— The  sand-hills  in  Nebraska  represent 
dunes  which  have  become  fixed  and  are  approaching  a  stable 
condition.     The    beard-grass    (Andropogon    scoparius),    one    of 
the  bunch-grasses,  is  the  dominant  species,  and,  because  of  the 
severe  dry  conditions,  makes  an  open  formation,  while  on  the 
sand  plains  another  beard-grass  (Andropogon  furcatus),  also  a 
bunch-grass,  is  the  dominant  one,  and  the  formation  is  closer, 
though   sometimes   open.      The   sand-plains   thus   represent,   as 
we  would  expect,  a  transition  from  the  true  prairie  areas  to  the 
more  xerophytic   condition  of  the  sand-hills.     What   are   called 
"blowouts"   are   formed  by  the  wind   where   the   sand-binding 
plants  have  been  uprooted.     They  are  similar  to  the  troughs  or 
gullies  formed  in  other  dune  regions  (see  Chapter  LIV). 

1050.  Subordinate  to  the   bunch-grasses  in  the    sand-hills 
are  xerophytic  shrubs,  herbs,  and  other  grasses.     The  sand-hills 
vegetation  may  be  looked  on  as  edaphic  formations  in  the  prairie 


562 


RELATION1    TO  ENVIRONMENT. 


region.  Since  the  grasses  are  the  dominant  species,  they  con- 
stitute the  fundament  of  the  formation.  Other  subordinate 
grasses  occur,  and  besides,  the  prairie  is  variegated  by  annual 
and  perennial  herbs  which  give  the  formations,  especially  in 
the  lower  areas,  a  spring  or  vernal  flora,  as  the  cat's-foot  (Anten- 
naria  campestris),  fennel-leaved  parsley  (Peucedanum  fcenicu- 
laceum),  prairie  clovers,  etc.;  and  a  summer-autumnal  flora,  as 
golden-rods,  verbenas,  amorpha,  etc. 

1051.  The  Bad  Lands  of  Nebraska  and  South  Dakota.— The 
vegetation  in  the  "Bad  Lands"  is  very  meagre  and  is  rendered 
so  for  several  reasons:  the  alkalinity  of  the  soil,  which  retards 


Fig.  5066. 

Bad  Lands.  Firms  ponderosa  scopularum  on  the  talus  of  buttes  on  the  borders 
of  Sowbelly  Canyon,  Pine  Ridge,  Nebraska.  Bouteloua  oligostachya  (grama 
grass)  formation  in  foreground.  (Dept.  Geol.,  Univ.  Nebr.) 

absorption  by  the  roots;  the  loose  and  crumbling  condition  of 
the  soil,  which  permits  active  erosion  during  rains  and  renders 
stability  of  any  plant  precarious;  the  very  dry  air  and  intense 
heat,  inducing  rapid  transpiration;  all  these  conditions  well 
nigh  prohibit  plant  life.  The  Bad  Lands  are  situated  in  and 
near  the  foot-hills  in  the  western  part  of  these  States.  There 


VEGETATION   OF   THE   PRAIRIE. 


563 


are  pyramidal  or  conical,  flat-topped  hills  (buttes)  with  very 
precipitous  sides,  and  between  them  canyons.  The  sides  of 
the  buttes,  cliffs,  and  canyons  erode  rapidly  during  rains.  The 
characteristic  plants  are  the  greasewood,  a  spiny  shrub  (Sar- 
cobatus  vermiculatus)  a  meter  (3  ft.)  or  less  in  height,  and  the 
white  sage  (Eurotia  lanata),  which  also  occurs  on  the  high  table- 


Fig.  so6c. 

Big  Bad  Lands  of  South  Dakota,  an  intervale  with  well-established  vegetation 
of  grasses,  shrubs,  and  trees.  (Dept.  Geol.,  Univ.  Nebr.) 

lands,  while  a  few  bunch-grasses  and  herbs  are  rare  or  occasional 
wanderers  from  the  outlying  districts. 

1052.  Alkaline  marshes  and  salt  basins. — Here  and  there  is? 
the  salty,  alkaline  basins,  meadows  are  formed  by  the  sod-grass, 
Distichlis  spicata  stricta,  and  Agropyron  pseudorepens.  In 
some  of  the  very  salty  ponds  in  the  basins,  Ruppl?  occidentalis, 
in  others  the  glasswort  (Salicornia  herbacea)  grows,  while  in  the 
salty  soil  around  the  basins  certain  chenopods  (species  of  Atri- 
plex),  also  the  bugseed  (Corispermum)  and  other  halophytes 
occur,  while  farther  out  are  the  salty  meadows  of  certain  sod- 
grasses.  Halophytes,  of  course,  are  able  to  flourish  in  a  soil 


564  RELATION    TO   ENVIRONMENT. 

or  water  with  a  concentration  which  would  kill  most  meso- 
phytes.  Some  plants  adapt  themselves  to  a  much  wider  range 
in  the  chemical  condition  of  the  soil,  for  example,  the  cheno- 
pods,  greasewoods  (Sarcobatus),  low,  much-branched  shrubs  oi 
radiate  habit,  spiny  branches,  and  small  linear,  fleshy  leaves,  etc. 
These  are  plants  which  grow  well  in  the  so-called  alkaline  soils, 
and  also  grow  in  ordinary  clay  or  loam  soils.  Some  soils  and 
waters  are  so  strikingly  different  in  chemical  conditions  that  the 
vegetation  is  profoundly  influenced. 


CHAPTER  LIT. 

DESERT    PLANT   SOCIETIES. 

I.  Characters  of  True  Desert  Plants. 

1053.  The  true  desert  plants  are  the  perennials  which  must 
preserve  stem  and  root  system  through  the  hot  dry  period.  They 
possess  a  habit  and  structure  the  result  of  the  operation  of  phys- 
iological causes  which  enable  them  to  exist  during  the  severe 
season.  They  are  xerophytes,  and  their  structures  are  xero- 
phytic,  i.e.,  those  which  fit  them  for  existence  where  the  climate 
is  dry,  or  where  there  is  difficulty  in  absorbing  water  from  the 
ground.  In  the  desert  this  difficulty  of  absorption  arises  from 
the  very  small  amount  of  water  in  the  soil.  Desert  plants  then 
have  to  meet  two  general  conditions,  a  very  dry  and  hot  atmos- 
phere and  a  very  dry  soil.  This  they  do  by  provision  for:  ist, 
reduction  of  transpiration;  2d,  provision  for  water-storage;  and 
3d,  increased  surface  for  root-absorption. 

1.  Reduction  of  transpiration.  —  This    is    brought    about    in 
several  ways:   ist,  by  reduction  in  size  so  that  the  leaves  are 
smaller  and   thicker;    2d,  by  hairy  coverings;    3d,  the   stomates 
are  sunk  deeply  in   the   surface;  4th,  the  cuticle  is  thickened; 
5th,  the  leaves  are  entirely  dispensed  with  and  the  stems  are  green 
and  function  as  leaves;  6th,  the  stems  are  shorter,  and  with  a 
thick  cuticle  and  often  hairy  or  waxy  coverings. 

2.  Provision  for  water-storage. — This  is  provided  for  by  thick 
and  often  fleshy  leaves,  by  fleshy  stems  as  in  the  cacti,  and  often 
by  a  thick  root  system.     Some  of  the  cacti  have  large,  rounded, 
globose  sterns.     Some  other  plants  have  large,  swollen  bases  to 

565 


566  RELATION   TO   ENVIRONMENT. 

their  stems,  and  in  others  the  roots  are  also  much  enlarged. 
These  types  with  enlarged  roots  are  rather  rare  in  the  Sonora- 
Nevada  desert  in  the  southwestern  part  of  the  United  States, 
but  are  more  common  in  southwestern  Africa  and  in  western 
South  America. 

3.  Increased  surface  for  root-absorption. — This  is  provided  for 
by  the  great  length  of  the  root  system  and  the  profuse  branching. 


Fig.  507- 

Desert  vegetation,  Arizona,  showing  large  succulent  trunks  of  cactus  with  shrubs 
and  stunted  trees.     Open  formation.     (Photograph  by  Tuomey.) 

In  many  desert  plants  the  roots  extend  to  great  depths  in  the  soils, 
where  they  obtain  ground-water  which  is  not  so  available  nearer 
the  surface. 

1054.  Thorny  or  spiny  character  of  desert  vegetation.— The 
development  of  thorns  and  spines  on  most  desert  plants  is  very 
striking.  The  cacti  are  remarkable  for  the  great  profusion  of 
spines  on  the  surface  of  their  stems.  The  small  leaves  of  many 
of  the  shrubs  are  sharp-pointed,  and  thorns  are  very  character- 
istic of  the  shrubs  of  dry  countries. 


DESERT   VEGE7-ATION-.  $6? 

1054a.  Conditions  of  environment  in  the  desert.— We  under- 
stand that  the  conditions  of  environment  are  very  austere,  so 
that  plant  life  comes  in  sharp  competition  with  the  climate. 

The  principal  factors  are: 

ist,  the  very  low  rainfall,  varying  from  8  to  10  inches,  in  some 
deserts,  to  4  inches,  or  even  less  than  i  inch  in  some  areas 
(see  paragraphs  926,  928,  933,  1060). 

2d,  the  great  amount  of  evaporation  during  the  long  dry  hot 
season;  the  amount  of  evaporation  from  the  soil  will  depend 
on  the  character  of  the  soil  and  the  amount  of  ground-water, 
some  soils  conserving  water  more  than  others. 

3d,  the  alternation  of  rainy  and  dry  seasons,  the  rainy  season 
in  the  temperate  regions  usually  occurring  during  the  cold  part 
of  the  year,  when  plants  cannot  make  use  of  it. 

Some  of  the  minor  factors  which  might  be  mentioned  are 
as  follows: 

ist,  the  strong  light  (solar  radiation),  especially  during  the 
warm  season.  This  is  due  to  the  absence  of  clouds  which  form 
a  blanket  over  the  earth,  not  only  cutting  off  direct  solar  radiation 
during  the  day,  but  which  also  check  radiation  of  moisture  from 
the  soil  both  during  day  and  night. 

3d,  high  winds,  which  often  sweep  over  desert  areas,  increas- 
ing the  drying  effect  of  the  air  on  vegetation. 

4th,  the  physical  or  chemical  character  of  the  soil  often  is 
such  as  to  enforce  a  xerophytic  habit  for  vegetation  even  if  rain- 
fall were  greater;  for  example,  salty  or  alkaline  condition  of  the 
soil,  calcareous  soils  in  some  desert  or  semi-desert  areas,  the 
loose  and  crumbling  condition  of  soil  in  some  regions  which 
permits  the  rapid  filtering  away  of  storm-  and  ground-water, 
the  topography  of  the  region;  also  when  very  rolling  or  hilly, 
permits  rapid  run-off  of  storm-water. 


568  RELATION   TO  ENVIRONMENT. 


II.  The  Sonora-Nevada  Desert. 

1055.  In  the  valley  between  the  Sierra  Nevada  and  Rocky 
Mountains,  including  the  Great  Basin  Ranges  of  Arizona,  Utah, 
southern  Nevada,  and  the  southern  part  of  California,  etc.,  which 
is  a  part  of  the  Sonoran  arid  area,  a  true  desert  condition  exists, 
shown  by  the  low  annual  precipitation,  as  well  as  by  the  dry 
hot  climate  and  the  great  amount  of  water  evaporated  from  the 
ground,  though  parts  of  it  are  intensified  by  the  salt  or  alkaline 
basins,    which    would    enforce    a    xerophytic    habit    irrespective 
of  the  dry  hot  climate.     The  desert  areas  are  not  determined 
alone  by  the  low  annual  precipitation.     A  hot  dry  climate  during 
a  large  portion  of  the  year  is  an  equally  great  factor.     A  district 
in  the  cooler  porticns  of  the  north  temperate  zone  with  a  low 
annual  rainfall    distributed    through    the    growing    season    may 
furnish  a  luxuriant  vegetation  with  no  true  desert  vegetation. 
On  the  other  hand,  a  district  with  an  equal  annual  rainfall  farther 
south,  where  the  climate  is  hot  and  dry  for  a  large  portion  of  the 
year,  and  the  rainfall  is  principally  during  the  cold  winter  season, 
may  have  a  true  desert  vegetation.     In  the  dry  hot  season  evapo- 
ration of  water  from  the  soil  is  very  great.     The  Desert  Botanical 
Laboratory  of  the  Carnegie  Institution,  established  near  Tucson, 
Arizona,  will  give  an  opportunity,  long  needed,  for  more  careful 
studies  of  the  desert  flora. 

1056.  In  the  "  Death's  Valley"  (within  the  area  of  this  desert) 
the  true  desert  portions  are  quite  distinct  in  vegetation  from 
the  areas  bordering  on  ponds  or  streams,  or  from  the  basins 
where  there  is  such  an  accumulation  of  water  as  to  provide  a 
sufficient  amount  of  ground-water  (hydrostatic  water)  to  support 
a  more  luxuriant  vegetation  even  through  the  dry  season.     These 
true  desert  portions  are  on  the  higher  area,  dry  ground,  and 
according  to  Coville  are  entirely  devoid  of  hydrostatic  moisture. 
All  the  water  they  receive  is  the  storm-water  during  the  rainy 
season  which  occurs  roughly  from  December  to  March.     The 
rains  during  this  period  amount  to  about  10  cm.  (4  inches).     The 


DESERT    VEGEJ^ATION.  $69 

water  is  absorbed  and  held  by  capillarity  of  the  soil  for  a  depth  of 
perhaps  several  feet. 

1057.  The  rainy-season   flora   thus   appears   in  later  winter 
and  early  spring.    The  seeds  germinate  along  about  February. 
When  the  rainy  season  closes  the  water  held  in  capillarity  by 
the  soil  begins  to  evaporate  under  the  influence  of  the  dry  air  and 
hot  sun.     The  loss  of  this  water  is  increased  by  transpiration  of 
most  of  the  water  absorbed  by  the  vegetation  which  has  sprung 
up  under  the  influence  of  the  rains  and  warm  spring.     Sometimes 
in  April  the  capillary  water  in  the  soil  has  all  been  withdrawn. 
The  annual  plants  in  the  meantime,  feeling  the  lessening  amount 
of  moisture  in  the  soil,  mature  and  ripen  their  seed,  and  then 
die,  while  the  perennials  prepare  for  the  period  of  rest,  by  the  loss 
of  their  leaves  or  the  death  of  their  aerial  parts.     They  are  sus- 
tained through  the  dry  hot  summer  and  autumn  solely  (Coville 
suggests)  by  hygroscopic  moisture,  i.e.,  that  which  the  now  air- 
dry  soil  absorbs  during  the  night  from  the  very  small  amount  of 
moisture    in    the    air.      There    are    occasional    summer    storms 
(amount  to  about  ^cm  water),  but  usually  so  slight  that  the  pre- 
cipitation is  immediately  re-evaporated  into  the  dry  air.     As  the 
rains  begin  again  in  December  a  few  of  the  perennials  bloom,  but 
the  season  is  then  too  cold  for  most  of  the  vegetation  to  flourish. 

The  annuals  are  the  best  adapted  of  any  plants  for  the  life  in 
the  desert,  since  the  growth  period  is  confined  to  the  rainy  season 
and  the  seed  carries  the  life  over  the  dry  period  and  the  cold  of 
winter.  The  seed  is  practically  the  only  adaptation  for  tiding 
the  plants  over  the  severe  dry  period,  since  the  leaves  are  usually 
soft  and  thin  and  none  are  succulent.  The  adaptation  is  the  same 
as  many  annuals  in  the  cool  temperate  regions  have  for  passing 
the  winter. 

1058.  Sand-dunes  in  the  desert.— In  the  Tularosa  district  of 
the    desert    in  New  Mexico,  these    drifting   sand-dunes  occupy 
an  area  of  10  by  40  square  miles,  and  the  sand  here  is  composed 
of  gypsum.     These  dunes  reach  a  maximum  height  of  60  feet. 
The  most  characteristic  plant  of  the  dunes  is  the  three-leaf  sumac 
(Rhus  trilobata).     The  cover  afforded  by  the  mat  of  branches  and 


570 


RELATION    TO   ENVIRONMENT. 


leaves  as  well  as  the  binding  effect  of  the  profusely  branching 
roots  often  holds  the  sand  in  place  in  the  form  of  tall  columns  as  the 
wind  moves  the  surrounding  portion  forward.  Other  charac- 
teristic woody  plants  are  Atriplex  canescens,  Yucca  radiosa,  etc. 
This  Yucca  is  sometimes  buried  by  dunes  and  seems  to  have  the 
power  of  growing  out  at  the  top  again  as  it  is  buried  from  time 
to  time  with  the  increasing  height  of  the  dune. 

1059.  The  true  desert  flora. — The  shrubs  have  the  compact 
rounded  growth,  and  small,  thick,  gray  leaves  peculiar  to  most 


Fig.  508. 

Sage-brush  (Artemisia  tridentata),  showing  open  formation  in  desert,  Arizona. 
(After  Schimper.) 

perennial  desert  plants,  since  their  relation  is  confined  to  the 
physical  forces  of  environment,  not  at  all  to  the  organic,  because 
the  formation  is  an  open  one.  The  height  of  the  shrubs  is  rarely 
over  i-i.5m  (3-4^  feet),  and  is  usually  less.  The  sage-brush 
(Artemisia  tridentata),  one  of  the  largest  shrubs,  barring  accidents, 
never  dies,  for  there  are  numerous  shoots  from  the  subterranean 
stock,  and  as  the  older  ones  die  they  bend  outward  and  down- 


DESERT   VEGETATION. 


571 


ward  while  new  shoots  are  developed.  Peucephyllum  schattii, 
on  the  other  hand,  is  tree-like  in  habit,  having  a  common  trunk, 
and  thus  in  old  age  dies.  These  two  shrubs,  according  to  Co- 
ville,  represent  the  two  types  in  the  Death's  Valley. 

The  perennial  vegetation,  aside  from  the  true  shrubs,  is  pecu- 
liar. Only  a  few  species  have  enlarged  roots  for  water  storage 
during  the  dry  season.  In  these  the  aerial  stems  die  down  to 
the  ground.  A  large  number  of  them,  however,  are  suffrutes- 
cent,  i.e.,  the  lower  portion  of  the  aerial  shoots  is  shrubby.  These 
remain  green,  and  slow  transpiration  goes  on  during  the  dry 
period,  as  in  the  case  of  the  true  shrubs,  while  the  roots  are  not 
thickened  for  water  storage,  but  find  enough  hygroscopic  water 
to  supply  the  reduced  shoot  system. 


Fig.  509. 
Desert  society,  chiefly  yucca. 


Cacti,  Yuccas,  etc. — Trees  are  not  present  in  the  true  desert 
portions  of  the  regions,  while  around  springs  or  along  streams, 
or  in  the  vicinity  of  basins  where  there  is  ground-water  through- 


5/2  RELATION   TO   ENVIRONMENT. 

out  the  dry  season,  trees  are  present,  especially  the  mesquite 
trees.  Tree  yuccas  (Y.  arborescens,  etc.)  occur  on  higher  ele- 
vations, but  not  on  the  lower  dry  ground.  These  yuccas  on  the 


Fig.  510. 

Winter  range  in  northwestern  Nevada,  showing  open  formations;  white  sage 
(Eurotia  lanata)  in  foreground,  salt-bush  (Atriplex  confertifolia)  and  bud-sage 
(Artemisia  spinescens)  at  base  of  hill,  red  sage  (Kochia  americana)  on  the  higher 
slope.  (After  Griffiths,  Bull.  38,  Bureau  Plant  Ind.,  U.  S.  Dept.  Agr.) 

mountain  slopes  are  just  beneath  the  coniferous  forest  line  which 
forms  a  horizontal  zone  on  the  mountain  slopes,  marking  the 
lower  limit  of  snowfall  in  a  very  sharp  manner  from  the  lower 
zone  of  rainfall.  The  snow-storage  here  on  the  desert  mountains 
provides  a  source  of  water  which  is  doled  out  later  in  the  season 
and  permits  the  forest  growth.  The  tree  yuccas  just  beneath 
this  forest  probably  get  some  of  this  moisture.  Besides  the 
plants  mentioned  above,  cacti,  salt-bushes  (Atriplex),  grease- 
woods  (Sarcobatus),  etc.,  occur.  These  all  show  the  usual 
adaptations  to  desert  conditions,  reduced  leaf  and  stem  surface 
to  check  transpiration,  and  an  increase  of  the  root  system  for 
absorption.  The  extent  to  which  the  reduction  of  surface  for 
transpiration  is  carried  in  desert  plants  and  the  corresponding 
increase  of  root  system  for  absorption  is  shown  by  Coville  in  the 
case  of  a  prickly-pear  cactus  examined.  The  aerial  part  con- 


DESERT    VEGETATION. 


573 


sisted  of  two  branching  stems  q&cm  (19  in.),  which  consist  of 
cylindrical  to  flattened,  pear-shaped,  thick,  succulent  portions 
devoid  of  leaves,  provided  with  a  thick  cuticle  and  large  water- 


Fig.  Si  I- 

Desert  vegetation    Arizona,  showing  clump  of  prickly-pear  cactus  in  foreground 
with  radiate  shrubs  in  background.    Open  formation.    (Photograph  by  Tuomey.) 

storage  system.     There  were  eight  roots  with  an  average  length 
of  2-$m  (7-10  feet),  each  of  which  had  numerous  lateral  branches. 


III.  Other  Desert  Regions. 

1060.  The  greatest  desert  region  in  the  world  comprises  the 
great  Sahara  Desert,  which  extends  across  the  northern  part  of 
the  continent  of  Africa  between  20°  and  30°  north  latitude,  and 
then  extends  over  Arabia,  then  southward  over  south  Persia 
and  Beluchistan  and  the  northeast  corner  of  farther  India. 
The  next  in  size  is  in  central  Asia,  from  the  Caspian  Sea  to  the 
mountains  which  separate  Mongolia  and  Manchuria.  The 
largest  one  in  the  southern  hemisphere  is  in  central  Australia; 
there  is  a  smaller  one  in  southwest  Africa,  and  a  narrow  desert 


574  RELATION   TO  ENVIRONMENT. 

on  the  west  coast  of  South  America  from  5°  to  30°  south  latitude. 
The  annual  rainfall  in  these  deserts  varies,  does  not  exceed  yocm 
(12  in.),  while  it  is  usually  much  lower,  from  $-8>cm  (2-3  in.), 
and  in  one  place  in  Chili  it  is  as  low  as  icm.  In  the  great  desert 
of  north  Africa,  and  its  continuation  in  southwestern,  Asia,  the 
annual  rainfall  is  about  2ocm  (8  in.). 

1061.  Time  of  maximum  rainfall. — The   maximum   rainfall 
occurs  at  different  seasons  in  different  deserts;    for  example, 
during  the  spring  in  Sahara,  autumn  in  north  Chili,  summer  in 
Australia.     The  rainfall  is  so  slight  that  the  vegetation  periods 
(except  the  rainy-season  flora)  are  independent  of  the  maximum, 
but  they  are  dependent  upon  temperature, .  and  the  austere  period 
occurs  during  the  hottest  period  of  the  year.     (In  Sahara  the 
July  temperature  rises  to  36°C.  =  97°F.)     According  to  Schim- 
per  the  vegetation  is  more  dependent  on  the  ground-water  than 
on  the  moisture  from  rainfall,  though  there  is  a  general  ephemeral 
rain  flora  in  the  spring.     When  the  rainy  season  is  over  the  green 
covering  of  the  earth  disappears,  and  the  ground  is  as  nearly 
devoid  of  plant  life  as  before.     Many  perennials  are  also  bene- 
fited   by    the    spring    rains,    chiefly    because    transpiration    is 
checked. 

1062.  Character   of  Sahara   Desert.— The    great    desert    of 
Sahara  consists  of  elevated,  furrowed,  and  stony  plains,  or  rolling 
and  stony  lands,  sandy  lowlands,  long    sand-dunes,  with   here 
and  there  an  oasis.     Strange  as  it  may  seem,  the  places  are  rare 
where  vegetation  is  not  in  sight  from  any  point,  but  this  consists 
of  low,   compact,   shrubby  plants  in  small  clusters  or  streaks. 
The  oases  are  populated  by  a  rank  growth  of  trees  and  herbs  and 
parts  of  them  are  cultivated.     The  line  between  oasis  and  desert 
is  closely  drawn. 

1063.  Two  ecological  vegetation  types  in  the  desert.— The 
plants  of  the  desert  may  be  grouped  into  two  ecological  cate- 
gories: the  existence  of  the  one  is  dependent  directly  on  the  rain-, 
the  other  on  ground-water,      ist.  To  the  first  category  belong 
the    rainy-season    plants.      They    germinate    their    seeds,    grow, 
flower,  and  seed  again  during  the  period.      There  are  also  per- 


DESERT    VEGETATION. 


575 


ennials  which  at  the  same  time  develop  foliage  stems,  flowers,  and 
fruit  during  the  rainy  season,  and  then  the  exposed  parts  die 
and  the  subterranean  rootstocks  carry  the  plant  through  the 


Fig.  5110. 
Desert  society,  chiefly  cactus,  Arizona. 


(Photograph  by  Tuomey.) 


dry  period.  2d.  The  plants  dependent  on  ground-water  belong 
to  the  second  category.  They  are  all  perennial  and  have  per- 
ennial aerial  shoots.  They  bloom  during  the  dry  cool  weather. 


CHAPTER   LIII. 

ARCTIC   AND   ALPINE    PLANT   SOCIETIES. 

I.  Arctic  Plant  Societies. 

1064.  The  arctic  zone  of  plant  life  extends  from  the  limit  of 
tree  growth  to  perpetual  ice  and  snow.     The  arctic  zone  is  some- 


Fig.  512. 

Northern  limit  of  tree  growth,  Alaska.     (Copyright,  1899,  by  E.  H.  Harriman.) 

times  spoken  of  as  the  "cold  waste,"  because  in  general  there 
are  some  of  the  aspects  of  the  desert  in  the  character  of  the  vege- 
tation.    The  analogy,  however,  is  not  fully  carried  out  because 
576 


ARCTIC    VEGETATION.  577 

the  effect  of  environment  is  not  wholly  similar.  The  ground 
over  a  large  part  of  the  region  is  frozen  to  a  great  depth  and  only 
thaws  out  on  the  surface  during  the  summer.  This  makes  the 
ground-water  usually  very  cold  even  during  the  summer. 

1065.  Character  of  tree  growth. — The  polar  limit  of  tree 
growth  is  conditioned  by  drying  winds  in  frosty  weather.  There 
is  no  sharp  dividing-line  between  the  forest  and  treeless  waste, 
but  there  is  a  gradual  reduction  in  the  number  of  the  trees,  their 
size  as  well  as  their  vigor.  The  formation  becomes  more  and 
more  open,  the  trees  are  reduced  more  and  more  in  size,  and  are 
more  and  more  disfigured  by  dead  and  dying  branches  and  tops, 
and  by  dwarfing  and  warping  out  of  shape  as  one  approaches 
the  true  polar  waste.  The  transition  line  is  gradual,  and  the 
two  climatic  formations  are  mixed.  Where  the  snows  are  not 
sufficient  to  cover  the  trees  for  several  months  during  the  winter 
the  tops  of  the  trees  die,  often  at  quite  a  regular  distance  from 
the  ground.  These  trees  often  branch  below  and  sprout  from 
below  and  thus  form  broad  expanded  low  crowns.  Where  the 
fall  of  snow  is  heavy  the  trees  are  often  covered  for  several  months 


Fig.  513. 

Polar  limit  of  tree  growth  in  Saghalin  near  Kamtchatka.  Large  trees  stunted 
and  showing  horizontal  growth.  Induced  by  high  wind  and  weight  of  snow. 
(After  Schimper.) 

during  the  winter.     The  snow  bends  the  tops  over  and  the  tree 
grows  more  or  less  horizontally.     The  covering  of  snow  and 


578  RELATION   TO  ENVIRONMENT. 

their  prostrate  condition  protect  them  from  the  drying  effect  of 
the  fierce  winds  in  the  very  cold  weather.  As  one  passes  be- 
yond the  line  of  tree  growth  the  trees  and  shrubs  become  greatly 
stunted  and  dwarfed.  Growth  in  length  of  the  stems  takes 
place  proportionally  slower  than  growth  in  diameter,  and  yet 
even  the  diameter  increases  very  slowly.  For  example,  a  dwarf 
tree  83 mm  (3^  in.)  in  diameter  showed  544  annual  rings! 

1066.  The  polar  tundra.— Tundra  is  the  name  given  to  a 
large  portion  of  the  polar  waste.  The  tundra  are  related  in 
their  formation  to  heath  or  peat  moors.  Heaths,  saxifrages? 
dwarf  willow,  and  other  dwarf  shrubs  abound.  The  forma- 


Fig.  514- 
Polar  tundra  with  scattered  flowers    Alaska.     (Copyright  by  E.  H.  Harriman.) 

tions  are  often  open,  and  the  vegetation  varies  over  different 
areas.  In  some  places  devoid  of  shrubs  the  tundra  is  covered 
with  a  growth  of  mosses  and  lichens,  often  the  reindeer-moss 
(Cladonia  rangiferina)  being  very  abundant.  So  there  are 
"moss- tundra"  (chiefly  the  moss  Polytrichum)  or  "lichen- 


ARCTIC   VEGETATION. 


579 


tundra"    (formed  of    different  species,   sometimes  Cladonia  or 
Alectoria,  etc.). 

1067.  Conditions  of  environment. — These  are  very  peculiar  to 
the  region,  ist.  Temperature,  the  extreme  cold  of  the  long  winter 
and  the  low  summer  temperature.  2d.  Light,  the  long  winter 
night  and  the  continued  daylight  of  the  short  cool  summer. 
The  continuous  light  in  the  summer  is  an  advantage,  since  photo- 
synthesis goes  on  without  interruption  and  food  materials  are 


Fig.  5140. 

Lichen  tundra  showing  the  "reindeer-moss"  or  lichen,  Alaska. 
E.  H.  Harriman.) 


(Copyright  by 


constantly  formed.  3d.  The  cold  ground-water  because  of  the 
ground-ice  below  the  shallow  layer  of  surface  soil  which  is 
thawed  out;  this  retards  root  absorption.  4th.  The  high  winds, 
which  in  the  cold  dry  climate  are  more  trying  for  plants  than 
the  lower  temperatures  to  which  they  are  subject.  5th.  The  very 
dry  air  of  the  long  winter.  The  long  winter  night  is  usually 
clear,  there  is  but  little  precipitation,  and  the  air  is  very  dry,  so 
dry  sometimes  during  the  severest  cold  that  one's  breath  does 


58o 


RELATION   TO   ENVIRONMENT. 


not  condense.  6th.  The  lessened  precipitation,  so  that  the  snow 
is  not  so  deep  except  in  colder  regions  where  it  does  not  all  melt 
during  the  summer,  but  forms  great  glaciers  or  permanent  snow- 
fields,  which,  of  course,  prohibit  plant  life  except  a  few  low 
organisms  on  the  surface  of  the  snow.  In  addition  the  high 


Fig.  515. 
Willows  from  Greenland,  one  third  natural  size. 

winds  often  drive  the  snow  from  extensive  tracts  and  leave  them 
bare  during  the  long  winter  night. 

1068.  Responsive  type  of  vegetation.— The  vegetation  responds 
to  these  conditions  of  environment  by  the  development  of  certain 
types  of  plants,  as  the  radiate  dwarf-cushion  type,  the  rosette 
type,  the  succulents,  etc.  The  succulents  are  plants  with  thick 
and  fleshy  stems  and  leaves  for  water-storage.  These  general 
characters  are  very  similar  to  those  of  many  desert  plants.  In 
plants  with  these  habits  there  is  less  radiation  of  heat  and  mois- 
ture, and  they  are  also  protected  better  from  the  drying  effect 
of  wind.  The  leaves  are  either  leathery,  stiff,  and  hard,  or 
small  scale-like  leaves  with  a  thick  cuticle,  as  in  Cassiope,  or 


ARCTIC   VEGETATION. 


58l 


needle-like  or  succulent,  as  in  the  saxifrages.     They  are  further 
protected  from  excessive  loss  of  water  by  the  stomates  being 


Fig.  516. 

Perennial  rosette  plant  from  alpine  flora   of  the  Andes,  showing  short  stem, 
rosette  of  leaves,  and  large  flower.     (After  Schimper.) 

sunk   in   cavities  or  covered  with   hairs  or   wax.     The  leaves 
of  grasses  resemble  those  of  grasses  of  the  arid  region. 

1069.  Resistance  to  cold. — Besides  these  adaptations  for  lessen- 
ing the  transpiration,  or  for  lessening  the  loss  of  water  when  the 
leaves  are  frozen,  the  plants  have  a  specific  power  of  resisting 
the  cold  which  is  probably  to  be  found  in  some  special  con- 
dition of  the  protoplasm. 

1070.  Flowers. — In  many  of  the  arctic  plants  the  flowers  are 
very  conspicuous.     They  are  in  general  brighter  in  color  than 
in  the  temperate  or  tropic  regions.     This  brilliancy  of  color  in 
the  flowers  has  been  noted  by  many  arctic  travellers.     Then  they 
are  usually  very  large  in  proportion  to  the  size  of  the  stem  and 
leaves,  often  large  flowers  being  found  on  herbs,  the  stems  of 
which  are  so  short  that  the  flowers  are  close  to  the  ground.     The 
summer  being  very  short,  the  period  for  growth  of  vegetation 
is  very  short,  from  two  to  two  and  a  half  months,  yet  in  this 
period  there  is  ample  time  for  flowering  and  fruit,  since  the  plants, 
being  perennial,  can  begin  at  once  to  form  flowers  in  the  early 
part  of  the  growing  season. 

1071.  Warm  oases.— There  are  even  "oases"  in  the  desert- 
like  tundra-wastes.     These  are  known  as  "warm  oases,"  situ- 


582  RELATION   TO   ENVIRONMENT. 

ated  where  they  are  protected  from  the  wind,  and  the  slope  of 
the  ground  is  such  that  the  sun's  rays  are  nearly  perpendicular 
to  the  surface.  The  ground  is  thawed  out  to  a  much  greater 
depth  and  the  ground-water  thus  becomes  much  warmer  than  in 
other  places.  This  encourages  a  more  luxuriant  growth  and  the 
protection  from  wind  also  favors  a  taller  vegetation.  The  result 
is  that  the  vegetation  in  these  places  stands  out  in  marked  con- 
trast to  the  usual  vegetation  type  because  of  the  height  and  lux- 
uriance of  the  growth. 


II.  Alpine  Plant  Societies. 

1072.  Alpine   plant  societies   occur  on  mountain  heights 

where  the  change  in  temperature  and  other  conditions  of  environ- 
ment are  so  great  as  to  produce  a  decided  change  in  the  vegetation 
type.  Schimper  treats  of  three  zones  of  vegetation  in  the 
mountain  regions  as  follows: 

1.  Basal  region,  where  the  vegetation  is  more  hygrophile,  and 
similar  to  that  of  the  lower  elevations  of   neighboring  lowlands 
because  of  the  increase  in  precipitation  at  the  lower  mountain 
elevation. 

2.  Montane  region,  where  the  vegetation  is  more  hygrophile 
and  less  thermophile  than  in  neighboring  lowland,  comparable 
to  the  vegetation  of  higher  elevations  of  lowlands  because  of  the 
increase  in  precipitation  induced  by  the  cool  mountain  region. 

3.  Alpine  region,  where   the   vegetation  is  influenced   by  an 
alpine   climate,   without   analogy  in   lowlands.     At  this  height 
precipitation  has  rapidly   diminished   and  is  less   than  in   the 
lowlands.     This  alpine  region  corresponds  to  the  alpine  zone 
of  the  forest  region,  according  to  Merriam. 

In  passing  from  the  base  of  mountains  to  the  lofty  summits, 
one  passes  rapidly  through  the  different  life  zones  corresponding 
to  the  change  in  climate,  the  forest  formations  showing  changes 
similar  to  those  seen  in  passing  from  the  austral  region  north- 
ward to  the  arctic  zone.  As  one  passes  upward  beyond  the 
tree-line  or  woodland  formation,  there  appears  a  grass-land 


ARCTIC  VEGETATION. 


583 


or  prairie  formation  which  is  a  transition  belt  to  the  true  alpine 
formation  above  and  which  is  comparable  to  a  desert  formation 
because  of  the  austere  conditions  which  so  limit  plant  growth. 
While  there  is  a  general  re- 
semblance between  alpine  and 
arctic  vegetation,  there  is  an 
essential  difference  in  structure 
even  of  individuals  in  the  same 
species.  As  a  matter  of  his- 
tory many  alpine  species  are 
arctic  species  which  were  left 
behind  as  the  continental  ice- 
sheet  retreated  northward  at 
the  close  of  the  glacial  peroid. 
Bonnier  has  found  that  aerial 
parts  of  Salix  polaris  and  Sax- 
ifraga  oppositifolia  are  more 
weakly  developed  in  polar  than 
in  alpine  individuals,  while  polar 
plants  in  general  have  thicker 
leaves  than  alpine  plants,  but 
the  leaves  of  polar  plants  show 
less  differentiation  in  structure 
and  larger  intercellular  spaces. 
So  the  present  form  and  struc- 
ture of  alpine  plants  are  not 
due  to  these  historical  causes, 
since  alpine  conditions  are 
sufficient  in  themselves  to  in- 
duce the  peculiar  habit  and  in  addition  to  induce  changes  in 
structure  since  the  glacial  period.  These  peculiarities  of  alpine 
plants  are,  therefore,  due  chiefly  to  physiological  causes  and  not 
merely  to  heredity. 

1073.  Factors  of  alpine  climate  influencing  plants. — These 
factors  are:  ist,  decrease  in  precipitation;  2d,  decrease  in  heat 
(the  temperature  being  very  low) ;  3d,  rarity  of  the  atmosphere, 


Fig.  517. 

Compact,  radiate  cushion  type  of 
vegetation  of  North  Polar  region, 
Draba  alpina.  (After  Kjellman.) 


RELATION   TO  ENVIRONMENT. 


which  favors,  4th,  strong  solar  radiation,  and  5th,  strong  radia- 
tion from  the  ground  bringing  about  great  changes  in  tempera- 
ture between  night  and  day;  6th,  the  high  winds;  ;th,  alter- 
nation of  night  and  day,  there  not  being  the  continuous  lighting 
present  in  polar  lands,  and  8th,  alternation  of  heat  and  cold 
during  the  growing  season,  again  very  different  from  the  arctic 
summer. 

1074.  Characters  of  alpine  vegetation. — The  characteristic 
alpine  vegetation  lies  above  the  limit  of  tree  growth,  which  often 


Fig.  518. 

Perennial  rosette  plant,  dandelion.  P,  lowland  culture;  M,  alpine  culture  pro- 
portionately same  size,  but  showing  difference  in  length  of  stem,  leaves,  and  the  larger 
root  of  alpine  plant.  (After  Bonnier. ) 

forms  a  very  distinct  line  on  the  mountainside.  The  vegeta- 
tion forms  are  similar  to  those  of  the  arctic  zone:  the  stems  are 
short,  the  leaves  smaller,  forming  rosettes  near  the  ground,  or 
scale-  or  needle-like  and  adpressed  close  to  the  stems.  The 
leaves  are  also  thicker,  often  protected  with  a  thick  cuticle  or  by 
a  covering  of  hairs,  and  the  structure  of  leaves  and  stems  is 
xerophile.  The  roots  are  usually  much  more  strongly  devel- 


ARCTIC   VEGETATION.  585 

oped.  The  flowers  are  often  large  in  comparison  with  the  stems 
and  leaves  and  have  usually  bright  colors.  Trees  and  shrubs 
are  dwarfed  and  stunted.  These  as  well  as  much  of  the  other 
vegetation  are  compactly  branched  and  of  the  rosette  or  radiate 
type.  The  mosses  form  dense,  deep,  and  extensive  cushions. 

1075.  Types  of  alpine  plants. — Schimper  distinguishes   the 
folio  wing  types:   ist.   Elfin  tree.  This  type  has  short,  gnarled,  often 
horizontal  stems,  as  seen  in  pines,  birches,  and  other  trees  growing 
in  alpine  heights.    2d.  The  alpine  shrubs.     In  the  highest  alpine 
belts  they  are  dwarfed  and  creeping,  richly  branched  and  spread- 
ing close  to  the  ground,  while  at  lower  belts  they  are  more  like 
lowland  shrubs.    3d.  The  cushion  type.  The  branching  is  very  pro- 
fuse and  the  branches  are  short  and  touch  each  other  on  all  sides, 
forming  compact  masses  (examples:  saxifrages,  androsace,  mosses, 
etc.).    4th.  Rosette  plants.     These  are  perennial,  with  short  stems 
and  very  strong  roots,  and  play  an  important  part  in  the  alpine 
meadows.    5th.  Alpine  grasses.    These  usually  have  much  shorter 
leaves  than  grasses  of  the  lowlands  and  consequently  form  a 
low  sward. 

1076.  Variation  of  individuals  of  same  species  in  alpine 
regions  and  lowlands. — It  is  believed  that  some  species  have  a 
very  wide  distribution  so  far  as  elevation  is  concerned,  so  that 
some  individuals  of  a  species  grow  in  the  lowlands  and  valleys, 
while    other   individuals  grow  also  in  the  alpine  region.     But 
the  form  of  the  plants  in  the  two  widely  separated  regions  is  so 
different  that  they  are  usually  regarded  as  distinct  species.     Ex- 
periments have  been  made  (especially  by  Bonnier)  in  transplant- 
ing alpine  plants  to  the  lowlands.     In  some  of  these  experiments 
single  alpine  individuals  were  divided,  one  half  taken  to  the 
lowlands  and  the  other  half  kept  in  the  alpine  regions,  while  the 
soil  used  in  both  cases  was  taken  from  the  lowlands.     In  a  few 
years  in  a  number  of  cases  the  halves  of  individuals  transplanted 
to  the  lowlands  took  on  the  form  of  lowland  species  which  were 
supposed  to  be  the  same,  while  the  halves  kept  in  alpine  climate 
underwent  no  change.     This  shows  that  at  least  some  of  the 
peculiarities  of  alpine  plants  are  due  to  the  alpine  climate. 


CHAPTER  LIV. 

THE   VEGETATION    OF   THE    STRAND. 

I.  Types  of  Strand. 

1077.  Strand  formations  are  usually  so  strikingly  different 
from  other  edaphic  as  well  as  from  climatic  formations  that  they 
may  be  considered  in  a  separate  section.  By  the  strand,  or 
beech,  flora  is  meant  the  plant  life  growing  along  shores  of 
the  water,  usually  lakes  or  seas.  There  are  two  general  types 
of  strand,  conditioned  by  the  water-holding  capacity  of  the  soil. 
These  are  the  ocerophytic,  or  dry  strand,  and  the  hydrophytic, 
or  moist  strand.  During  surf  action  or  rains  the  dry  strand 
is  wet,  but  in  the  sandy  soil  the  water  leaches  out  quickly  and 
also  evaporates  rapidly  from  the  surface,  while  on  rocks  the 
water  runs  quickly  off.  Radiation  of  heat  takes  place  more 
rapidly  also  from  a  sandy  soil  than  from  a  nitrophytic  soil,  i.e., 
one  with  an  abundance  of  humus.  In  the  xerophytic  strand  the 
gradient  of  the  slope  is  steeper,  so  that  there  is  only  a  narrow 
zone  of  shallow  water,  or  none,  while  in  the  hydrophytic  strand 
the  gradient  is  low,  giving  a  usually  broad  zone  of  shallow  water 
where  the  surf  breaks  before  reaching  the  shore  line.  Here 
there  is  usually  an  abundance  of  aquatic  vegetation,  and  some 
plants  in  this  zone  often  act  as  surf  barriers  (certain  species  of 
Cyperus,  the  flags,  etc.).  Between  these  two  types  of  strand, 
however,  there  are  all  gradations  and  modifications,  so  that  for 
purposes  of  study  a  farther  subdivision  is  desirable,  and  often 
different  strands  will  have  different  composite  elements,  so  that  a 

586 


VEGETATION  Of  THE  STRAND. 

classification  adapted  in  one  case  may  not  be  so  serviceable  in 
another.  For  example,  the  action  of  surf  on  the  strand  forma- 
tions will  be  different  on  the  shore  of  a  lake  not  frozen  over  during 
the  winter,  when  the  high  winds  carry  the  wave  action  higher  up 
than  in  the  summer.  Ocean  tides  also  tend  to  complicate  the 
strand  formations  beyond  what  is  seen  on  the  shores  of  lakes  or 
ponds.  Along  salt  bodies  of  water  also  a  halophytic  type  is 
developed  on  rocky  shores  and  in  salt  marshes,  and  to  a  limited 
extent  on  the  mid-strand  sandy  shores. 

The  flora  of  the  strand  bears  a  very  close  relation  to  its  physi- 
ography, and  can  only  be  understood  when  studied  in  connection 
with  the  physical  geography  of  the  region,*  and  in  an  endeavor 
to  trace  the  evolution  of  the  plant  formations,  i.e.,  the  part  which 
plants  have  played  in  determining  the  physical  geography  of 
the  strand,  as  well  as  the  influence  of  environmental  factors  on 
the  plant  formations. 

1078.  Variations  in  the  shore. — Variations  in  the  topography 
of  the  shore  offer  very  different  conditions  for  plant  life,  so  that 
a  great  variety  of  edaphic  formations  are  developed.  These 
variations  take  place  in  three  general  directions:  ist,  the  gradi- 
ent of  the  shore,  whether  precipitous  as  shown  in  the  bluff,  or 
very  high  steep  banks,  or  in  the  lower  grades  down  to  a  gradual 
slope  toward  the  interior  country;  2d,  the  mechanical  condi- 
tion of  the  shore  material,  whether  of  solid,  smooth-surface 
rock  or  creviced  rock,  boulders  large  or  small,  talus,  gravel, 


*  MacMillan  (1897)  was  the  first  one  in  America  to  apply  this  principle 
to  the  study  of  plant  formations.  (See  observations  on  the  distribution 
of  plants  along  the  shore  at  Lake  of  the  Woods.  Minn.  Bot.  Stud.,  Vol.  I., 
Bull.  9,  949-1023,  May,  1897.)  In  concluding  he  says:  "No  extended 
summing  up  is  necessary,  for  it  must  be  apparent  that  the  purpose  of  the 
paper  has  been  but  a  single  one — to  point  out  the  dependence,  over  such 
an  area  as  the  shores  of  the  lake,  of  plant  formations  upon  topographic 
and  environmental  conditions.  It  has  been  shown  how  each  formation 
may  be  explained  briefly  as  connected  with  a  certain  melange  of  outward 
conditions  both  by  themselves  and  as  connected  with  the  growth  of  the 
vegetation." 


$88  RELATION   TO  ENVIRONMENT. 

sand,  humus,  or  morass;  3d,  the  percentage  of  humus.  Varia- 
tions in  exposure  to  tides,  wave  action,  drainage,  and  winds 
affect  not  only  the  topography  of  the  shore,  but  also  the  develop- 
ment of  the  plant  formations. 

In  general,  then,  there  are  three  different  kinds  of  strand  as 
regards  the  physical  character  of  the  ground: 
i st.  Rocky  shores,  or  Lithophytic. 
2d.  Sandy  shores,  or  Psammophytic. 
3d.  Loamy  shores,  or  Humiphytic. 

The  first  two  condition  open  growth  of  vegetation  and  approach 
the  desert  type,  while  the  last  one  conditions  a  close  growth. 

The  first  and  third  types  will  be  treated  of  under  the  head 
of  the  various  rock  and  swamp  societies  (Chapter  LV). 

1079.  Formation  of  sandy  shores. — The  sand  of  the  sea  or 
lake  shores  is  formed  by  the  action  of  the  beating  waves  or  cur- 
rents on  rocky  shores;    or  the  grinding  action  of  rocks  on  the 
beds  of  streams  or  under  moving  glaciers.     From  streams  this 
is  washed  down  to  the  seas  or  lakes,  where,  if  the  shore  is  not  too 
precipitate,  it  is  deposited  where  the  wave  action  may  throw  it 
up  on  the  shore  and  form  the  sandy  beach.     So  wave  action  on 
rocky  sea  or  lake  coasts  grinds  the  rock  down  into  sand  in  places, 
which  is  again  washed  up  on  the  shore  to  form  the  sandy  beach. 
When  the  sand  accumulates  on  the  shore,  at  the  upper  edges, 
during  calm  periods  of  the  water,  it  dries  out  and  then  is  easily 
swept  inland  by  the  wind,  when  it  forms  fields  or  hills  of  sand 
known   as  sand-dunes.      The   vegetation  of  sandy   shores   can 
then  best  be  studied  under  two  heads:    ist,  the  vegetation  of  the 

beach  or  strand;   and  2d,  the  vegetation  of  sand-dunes. 

\ 

II.  The  Vegetation  of  the  Beach  or  Strand. 

1080.  Divisions  of  the  strand. — Sandy  shores  are  sometimes 
spoken  of  as  the  true  strand,  or  beach.     There  are  certain  natu- 
ral divisions  in  the  topography  of  the  beach,  due  largely  to  the 
action  of  the  water,  and  parallel  with  the  coast  line,   and  the 
plant  formations  are  found  to  bear  a  distinct  relation  to  these 


VEGETATION  OF   THE   STRAND.  589 

divisions.  Schimper  divides  the  ocean  strand  into  three  parts: 
ist,  the  fore-shore  (Schorre),  the  area  covered  by  the  tide  be- 
ween  ebb  and  flow,  and  in  sandy  shores  devoid  of  vegetation; 
2d,  the  mid-shore,  above  the  flood  line  of  the  tide;  3d,  the  dunes t 
he  sand-hills  toward  the  interior.  A  different  division  is  made 
>f  the  strand  formations  of  Lake  of  the  Woods  by  MacMillan 
as  follows: 

i  st.  The  front  strand,  being  that  part  of  the  strand  next  the 
water,  upon  which  the  surf  washes  during  the  ordinary  winds  of 
he  season.  2d.  The  mid-strand,  an  area  parallel  with  this,  but 
arther  up  on  the  beach  and  acted  upon  by  the  surf  at  greater 
ntervals  during  very  high  winds.  At  Lake  of  the  Woods  these 
igh  winds  are  believed  by  MacMillan  to  occur  once  in  several 
fears.  3d.  The  back  strand.  This  is  developed  by  the  activity 
>f  the  wind  rather  than  by  the  ice  or  surf,  and  may  represent  in 
ome  cases  a  higher  level  of  the  lake.  4th.  Strand  pools,  hollows 
,vhere  water  accumulates  either  from  surf  or  from  rains.  5th. 
Dunes,  hills  of  sand  formed  by  the  wind  driving  the  sand,  which 
s  caught  and  held  by  plants.  Some  use  a  slightly  different 
erminology,  as  follows: 

ist.  Lower  beach  (  =  front  strand);  2d,  middle  beach  (  =  mid- 
trand);  3d,  upper  beach  (  =  back  strand);  and  4th,  dunes. 

1081.  The  lower  beach,  or  front  strand. — This   being   fre- 
quently washed  by  the   surf  prevents   the  permanency  of  any 
vegetation.     Seeds  of  plants   may   germinate,   but   waves  wash 
the   seedlings  away.     The  only  plants  which   develop   here  are 
those  which  can  pass  through  the  period  of  growth  and  fruiting 
in  a  short  while.     Thus  lower  algae,  especially  members  of  the 
Cyanophycece  (blue-green  algae),  are  often  found  here  in  small 
pools  which  are  fed  by  the  surf.     If  the  water  remains  quiet 
for  some  time,  the  pool  may  dry,  but  the  plants  are  tided  over 
the  dry  period  by  their  spores  (Nostoc,  Anabaena,  Oscillatoria, 
Lyngbya,  etc.). 

1082.  Middle  beach. — This   corresponds   to  mid-strand,  and 
represents  the  zone  acted  upon  at  longer  intervals  by  the  surf, 
generally  during  the  winter  at  the  time  of  higher  winds.     The 


59°  RELATION    TO   ENVIRONMENT. 

conditions  are  severe  because  evaporation  of  water  and  radia- 
tion of  heat  are  rapid.  The  vegetation  is,  therefore,  sparse, 
scattered,  and  xerophytic.  Characteristic  sand  plants  along 
Lake  of  the  Woods,  like  certain  grasses  (Agropyron  tenerum, 
Elymus  canadensis)  and  other  sand  herbs  (Artemisia  caudata 
and  canadensis),  are  among  the  first  to  gain  a  foothold,  and 
species  in  these  genera  are  found  in  similar  strand  formations 
on  the  Great  Lakes  and  on  the  Atlantic  and  Gulf  coasts.  These 
assist  in  the  formation  of  humus  and  in  holding  it,  and  soon 
other  plants  appear.  The  formations  vary  greatly  according 
to  variations  of  soil  and  exposure.  Thus  one  with  considerable 
wind  exposure  has  as  a  dominant  plant,  a  low  shrub  with  small 
leaves,  Prunus  pumila,  the  sand-cherry  (Prunus  formation),  with 
subordinate  species  of  a  similar  habit,  as  well  as  sand  grasses 
and  herbs.  Another  formation  with  less  wind  exposure  and  a 
less  per  cent  of  humus  has  a  taller  shrub  with  broader  leaves  as 
the  dominant  plant  and  is  a  Cornus  formation.  In  still  another 
where  inundation  is  frequent  and  the  plants  would  be  more 
liable  to  be  torn  out,  certain  dwarf  willows  which  are  low,  small- 
leaved  and  deep-rooted  are  dominant,  and  this  is  the  Salix  for- 
mation, and  so  on.  While  all  these  formations  .are  adapted  to 
severe  conditions,  each  one  presents  peculiar  types  of  austere 
conditions  and  is  populated  with  dominant  plants  which  pre- 
sent special  adaptations  to  specific  conditions. 

On  the  east  shore  of  Lake  Michigan  the  dominant  plant  is  a 
crucifer,  American  sea-rocket  (Cakile  edentula),  while  two  others 
are  common,  bug-seed  (Corispermum  hyssopifolium)  and  sea- 
side spurge  (Euphorbia  polygonif olia) .  The  Cakile  and  Euphor- 
bia are  characteristic  also  of  the  beach  on  the  Atlantic  coast, 
while  on  the  Gulf  coast  or  island  shores  of  Mississippi  and  Louisi- 
ana low  succulent  plants  with  radiate  habit  of  growth  occur. 
There  is  here  a  seaward  zone  of  sea-blite  (Dondia  linearis),  sea- 
rocket  (Cakile  fusiformis),  saltwort  (Salsola  kali),  sea-purslane 
(Sesuvium  maritimum),  large  burr-grass  (Cenchrus  macrocepha- 
lus);  and  a  landward  zone  of  the  same  with  tropical  morning- 
glories  (Ipomoea  pes-caprae  and  I.  acetosaefolia)  trailing  on  the 


VEGETATION   OF   THE   STRAND.  59 1 

ground  for  30^  or  more,  the  trailing  wild  bean  (Strophostyles 
helvola).  These  trailing  morning-glories  occur  on  the  beach  in 
tropical  regions  of  South  America.  For  protection  against 
strong  insolation  (excessive  heat)  the  blade  of  the  leaves  is  brought 
nto  a  vertical  position.  The  trailing  wild  bean,  on  the  other 
land,  extends  as  far  north  as  Quebec  and  west  to  South  Dakota, 
Nebraska,  and  Texas  in  sandy  soil.  The  sea-rocket  and  salt- 
wort also  extend  northward  along  the  middle  beach  of  the  Atlan- 
tic coast  of  the  United  States. 

1083.  The  upper  beach  is  the  third  parallel  zone  and  corre- 
sponds probably  to  the  back  strand.     This  is  beyond  the  reach 
of  the  waves,  and  perhaps  in  some  cases  represents  a  former  por- 
ion  of  the  beach  acted  upon  by  the  surf,  though  it  is  principally 
developed  by  the  activity  of  the  wind.     The  limits  of  all  of  these 
sones  are  constantly  changing,  due  to  the  action  of  the  waves  on 
he  water  side  and  of  the  wind  on  the  landward  side.     Chemical 
and  physical  conditions  of  the  soil  are  also  different,  there  is  a 
ligher  percentage  of  humus,   shows  darker  color,  evaporation 
and  radiation  are  less,  the  soil  water  is  nearer  the  surface,  and 
he  soil  retains  more  heat.     This  encourages  different  biological 
xmditions  which  are  shown  in  the  different  character  of  the 
lants.     Though  sand  is  still  the  principal  constituent  of  the  soil, 
he  characteristic  plants  are  those  which  have  more  of  a  thermo- 
phytic  or  nitrophytic  character.     The  conditions  of  plant  life  are 
less  severe  than  on  the  middle  beach.     Still  the  vegetation  is 
similar  to  that  of  sand  formations,  and  the  nitrogenous  material 
is  not  so  abundant  as  to  encourage  true  humus  plants  like  Coral- 
lorhiza  or  Pyrola.     The  vegetation  of  the  upper  beach  may  also 
be  divided  into  several  formation  groups  according  to  certain 
soil   characters,    and   these   again   are    still   further   subdivided 
according  to  areas  which  encourage  certain  dominant  types  of 
plants,  whether  herbaceous,  shrubby,  or  arboreal,  and  these  fur- 
ther into  the  individual  formations.     According  to  Cowles  the 
most  characteristic  species  of  the  upper  beach  on  Lake  Michi- 
gan are:    ist.  Grasses  and  other  herbs.     Artemisia  caudata  and 
A.   canadensis,   while   these   are   often   associated   with   Cnicus 


592  RELATION    TO   ENVIRONMENT. 

pitcher! ,  Lathyrus  maritimus,  which  is  also  a  marine  beach 
plant,  Euphorbia  polygonifolia,  (Enothera  biennis,  and  Agro- 
pyron  dasystachyum.  2d.  Shrubs.  Of  the  shrubs  the  common 
ones  are  the  sand-cherry  and  a  species  of  willow  which  have  been 
noted  on  the  mid-strand  of  Lake  of  the  Woods.  3d.  Trees.  Of 
trees  the  cottonwood  occurs,  the  Populus  monolifera  southward 
and  Populus  balsamifera  northward. 

1084.  Wide  distribution   of  beach  plants.— The  full  list  of 
even  some  of  the  most  common  species  characteristic  of  the 
different  strand  zones  cannot  be  given  here,  but  it  is  interesting 
to  note  that  while  some  beach  plants  have  a  very  wide  distribu- 
tion, occurring  throughout  the  length  of  the  Atlantic  coast  and 
on  the  shores  of  the  Great  Lakes,  others  have  a  less  extensive  dis- 
tribution, so  that  in  the  tropical  and  subtropical  regions,  for 
example,  areas   occupied    by  certain  plants  in  the  boreal  and 
austral  regions  are  occupied  by  entirely  different  plants.      Thus, 
in   the   tropics,   Spinifex    squarrosus    and    Ipomcea    pescaprae 
occur  on  the  upper  beach,  the  latter  extending  as  far  north  as 
the  beach  of  the  island  flora  of  Mississippi  and  Louisiana. 

III.  Vegetation  of  the  Dunes. 

1085.  How  dunes  are  formed. — Dunes  are  mounds  or  hills 
of  sand,  lying  on  the  landward  side  of  the  beach.     They  are 
formed  by  the  sand  which  is  driven  from  the  upper  beach  and 
caught  in  the  stools  or  tufts  of  plants.     They  begin  by  the  col- 
lection of  small  piles  of  sand  about  tufts  of  certain  grasses;   for 
example,  marram-grass,  or  sea-matweed  (Ammophila  arenaria), 
the    northern    wheat-grass    (Agropyron    dasystachyum),    long- 
leaved  reed-grass  (Calamovilfa  brevipilis),  and  species  of  Andro- 
pogon,  Elymus,  etc.     As  the  dunes  grow  in  size  other  plants 
appear,  finally  an  open  formation  of  shrubs  and  trees  is  de- 
veloped, and  the  dunes  sometimes  become  of  considerable  size. 

1086.  Kinds  of  dunes.* — Dunes  are  described  as  stationary 


*  Cowles  has  made  an  interesting  study  of  the  dunes  on  the  eastern 
shore  of  Lake  Michigan  (Ecological  Relations  of  the  Vegetation  of  the 
Sand  Dunes  of  Lake  Michigan,  Bot.  Gaz.,  27,  1899). 


VEGETATION  OF   THE   STRAND.  593 

or  active,  or  stationary  ones  may  be  further  divided  into  embry- 
onic dunes  and  mature  dunes.  A  stationary  dune  is  one  that 
may  continue  to  increase  in  size,  but  does  not  actively  move 
from  place  to  place.  An  active  or  wandering  dune  is  one  that 
is  constantly  moving  from  the  action  of  the  wind  blowing  the 
sand  from  the  landward  to  the  leeward  side.  Embryonic  dunes 
are,  of  course,  young  ones,  and  there  is  no  distinct  line  to  be 
drawn  between  an  embryonic  and  an  old  or  mature  dune.  Then 


Fig.  519- 
Embryonic  dune,  shore  of  Lake  Michigan.     (After  Cowles.) 

one  might  speak  of  fossil  dunes  and  rejuvenated  dunes.  Fos- 
sil dunes  are  those  which  have  become  covered  for  years  by 
forest  and  where  dune  action  has  ceased  by  the  disappearance 
or  retreat  of  shores  where  wave  action  increases  the  amount 
of  sand.  Rejuvenated  dunes  are  old  dunes  which  have  sprung 
into  life  again. 

1087.  Dune-forming  plants. — Dune-forming  plants  must  pos- 
sess certain  biological  characteristics  which  enable  them  to  not 
only  live  under  these  very  severe  conditions,  but  they  must  also 
possess  the  habit  of  growing  in  mats  or  tufts,  or  with  the  stems 
and  branches  so  related  or  interlaced  as  to  check  the  force  of 
wind  and  cause  the  precipitation  of  the  sand  particles  and  afford 
the  sand  shelter.  Some  of  the  biological  characters  best  adapted 


594  RELATION    TO   ENVIRONMENT. 

for  this  purpose  are:  ist,  perennial  habit,  since  the  death  of 
an  annual  would  cease  to  afford  shelter  for  the  accumulated 
sand;  2d,  rhizome  propagation;  by  the  subterranean  stems 
the  plant  is  enabled  to  spread  and  increase  the  mat  and  thus 
afford  an  opportunity  for  enlargement  of  the  dune;  3d,  ability 
of  the  stems  to  grow  out  of  the  sand  when  buried;  4th,  highly 
developed  xerophytic  structures  to  endure  the  severe  conditions 
in  the  sand;  5th,  ability  to  stand  at  least  partial  root  exposure 
where  the  roots  on  the  windward  side  may  be  uncovered. 

The  best  dune-formers  as  found  in  the  Lake  Michigan  region, 
according  to  Cowles,  are  as  follows: 

1.  Grasses  with  rhizome  formation. 

Ammophila  arundinacea.     Most  abundant. 
Agropyron  dasystachyum  (northward). 

2.  Grasses  forming  clumps. 

Elymus  canadensis. 
Calamagrostis  longifolia. 

3.  Shrubs. 

Salix  adenophylla.     Most  abundant. 

Salix  glaucophylla. 

Prunus  pumila. 

Cornus  stolonifera  (or  C.  baileyi). 

4.  Trees. 

Populus  monolifera. 

Populus  balsamifera. 

1088.  Character  of  formations  on  dunes  of  different  size. — 
Very  often  embryonic  dunes  are  formed  on  the  middle  or  upper 
beach,  but  these  usually  are  temporary;  sometimes  those  on  the 
upper  beach  may  migrate  landward  and  grow  to  become  larger 
dunes.  In  general,  in  age  and  size  the  dunes  bear  a  definite  rela- 
tion to  the  shore-line,  the  younger  and  smaller  ones  lying  toward 
the  beach,  while  the  older  and  larger  ones  are  usually  landward. 
There  is,  however,  great  variation  in  size,  so  that  the  land  pre- 
sents often  a  hilly  or  wavy,  billowy  appearance.  The  forma- 
tions also  show  the  same  tendency  from  young  and  open  ones 
at  the  beach  to  the  older  and  often  closed  onse  on  the  older, 


VEGETATION   OF   THE   STRAND. 


595 


higher  dunes  landward.  There  is  also  a  corresponding  grada- 
tion in  the  size  of  the  vegetation  comprising  the  formations; 
grasses  and  lower  shrubs  with  a  very  open  formation  in1  the 
region  of  younger  dunes;  larger  shrubs  and  often  dense  thickets 
with  a  few  trees  in  the  middle  region  of  the  dunes  intermediate 


Fig.  520. 

Compact,  radiate  clumps  of  willow  on  sand-dunes  on  the  outskirts  of  the  city 
of  Southport,  England.  (Photograph  by  the  author.) 

in  size;  while  the  outer  landward  dune  region  is  often  occupied 
by  forests,  which  then  are  frequently  continuous  with  the  forested, 
sandy  plane  beyond. 

1089.  Active,  or  wandering,  dunes. — This  name  has  been 
applied  to  dunes  which  are  moving,  and  is  characteristic  of 
many  younger  and  growing  dunes.  Then  also  stationary  dunes 
may  change  to  active  ones.  One  of  the  reasons  why  a  station- 
ary dune  may  become  an  active  one  is  that  when  it  increases  in 
size  plant  life  is  limited,  owing  to  the  fact  that  the  plants  on 
the  surface  are  farther  from  the  soil  moisture,  since  the  sand 
does  not  retain  water  readily.  In  the  second  place,  some  of 
the  trees  on  dunes  in  certain  regions,  the  cottonwood  tree  for 
example,  is  of  comparatively  short  life,  and  the  same  is  true  of 
the  sand-cherry.  When  the  plants  die,  therefore,  the  top  of 
the  dune  on  the  windward  side  is  blown  off,  because  there  is 
no  vegetation  to  protect  and  hold  the  sand.  This  is  the  begin- 


RELATION    TO   ENVIRONMENT. 


VEGETATION  OF   THE   STRAND. 


597 


ning  in  the  movement  of  the  dune.  As  the  top  of  the  windward 
side  is  first  blown  off,  this  lowers  the  gradient  on  the  windward 
side,  until  finally  it  becomes  low,  having  about  5  per  cent  gradi- 
ent, while  the  gradient  on  the  leeward  side  is  that  which  fine 
sand,  where  not  disturbed  by  wind  or  wave  action,  takes  under 
the  influence  of  gravity  and  is  about  a  30  per  cent  gradient. 
These  wandering  dunes  are  often  very  complex;  since  several 
dunes  may  come  together,  troughs  may  be  ploughed  through  the 
dune  by  the  wind,  forming  gullies,  in  which  case  plants  are  un- 
covered. Then  smaller  dunes  behind  larger  ones  may  be  pro- 
tected from  the  prevailing  winds  which  come  from  the  water. 
These  may  move  in  any  direction  by  lesser  winds. 

1090.  Effect  of  wandering  dunes  on  the  landward  flora.— 
These  wandering  dunes  often  produce  very  great  changes  in  the 


Fig.  522. 

Encroachment  of  a  dune  on  old  and  long-established  oak-dune  at  Dune  Park. 
Dead  oak-trees  at  the  margin:     (After  Cowles.) 

landward  flora,  since  they  encroach  upon  the  plant  societies, 
and  high  ones  often  bury  the  vegetation,  or  the  mere  branches 
of  tree-tops  may  be  projecting  through.  In  many  cases  this 
kills  the  trees,  and  as  the  dune  moves  onward  the  dead  trunks, 


59$  RELATION    TO   ENVIRONMENT. 

some  left  standing  and  others  fallen,  are  sometimes  spoken  of 
as  "forest  graveyards"  in  the  track  of  the  dune.  These  are 
often  found  in  the  track  of  wandering  dunes  on  the  eastern 
shore  of  Lake  Michigan  and  also  on  the  Atlantic  and  Gulf  coasts. 
Wandering  dunes  often  encroach  upon  cultivated  fields  which  are 
near  the  coast  line,  and  thus  may  bury  valuable  arable  land. 

1091.  Rejuvenated  dunes. — As  stated  above  under  the  head  of 
kinds  of  dunes,  a  rejuvenated  dune  is  one  which  has  become 
old  and  inactive  for  a  period,  but  becomes  active  again  for  one 
or  more  reasons,  some  of  which  have  been  mentioned  above. 
Some  very  interesting  cases  of  rejuvenated  fossil  dunes  are 
known  in  New  York  not  far  from  Lake  Ontario. 

The  shore  line  of  the  great  lake  in  glacial  times  which  occu- 
pied the  present  site  of  Lake  Ontario  is  still  evident  as  a  promi- 


Fig.  523- 

Planting   grasses  on  wind-swept  sandy  coasts  to  prevent  movement   of  dunes 
into  the  city,  Southport,  England.     (Photograph  by  the  author.) 

nent  ridge  some  fifteen  to  twenty  miles  south  of  the  present 
shore.  In  some  places  in  Oswego  Co.,  N.  Y.,  according  to 
Professor  Rowlee,  are  sandy  elevations  which  were  formed  by 
dunes  on  the  shore  of  this  glacial  lake.  After  the  waters  receded 


VEGETATION   OF   THE   STRAND.  599 

these  dunes  finally  became  forested.  The  influence  of  man  is 
here  well  shown  in  some  cases  where  the  forest  has  been  cut  from 
these  fossil  dunes.  In  some  cases  the  land  thus  deforested  has 
been  pastured  by  sheep.  The  vegetation  was  thus  so  nearly 
removed  that  the  wind  has  been  able  to  play  upon  the  sand 
again,  resulting  in  extensive  " blowouts"  or  "dugouts,"  and  some 
of  these  old  dunes  have  sprung  into  life  again. 

1092.  Methods  for  checking  the  movement  of  dunes. — Suc- 
cessful efforts  have  been  made  in  some  cases  to  check  the  move- 
ment of  dunes  by  planting  grasses,  especially  those  species  which 
have  been  found  to  make  good  dune-formers.  Among  dune- 
formers  on  the  Gulf  coast  may  be  mentioned  the  salt  and  creeping 
panicums  (P.  halophilum  and  P.  repens),  sea-oats  (Uniola  panicu- 
lata),  and  the  seacoast  marsh  elder  (Iva  imbricata),  which  forms 
small  " pedestal"  dunes  according  to  Lloyd.  Along  the  Atlantic 
coast,  beach  plants  and  dune-formers  are  marram-grass  (Ammo- 
phila  arenaria),  sea-oats  (Uniola  paniculata),  sea-beach  panicum 
(P.  amarum),  and  the  seacoast  marsh  elder  (Iva  imbricata). 


CHAPTER  LV. 

PLANT    SOCIETIES    OF    ROCKY    AREAS,    MEADOWS, 
AND   MARSHES. 

I.  Vegetation  of  Rocky  Places  and  New  Land. 

1093.  Most  of  the  convenient  opportunities  for  the  study  of 
the  vegetation  of  rocky  places  are  in  the  later  stages  of  the  forma- 
tion.    We  rarely  have  an  opportunity  to  see  the  beginning  and 
to  watch  the  development  for  several  years.     Nevertheless  rock 
slides  occur  where  areas  of  bare  rock  are   exposed,  or  falling  rock 
at  the  base  of  a  cliff  may  form  a  recent  talus,  or  the  river  or 
stream  at  flood  may  wash  the  soil  from  a  rocky  area,  or  may 
pile  rocks  along  the  shore,  leaving  a  rock  area  small  or  large 
exposed  and  entirely  devoid  of  soil  or  vegetation.     These  places 
should  be  sought  out  and  observed  from  time  to  time.     In  lieu 
of  these  opportunities  one  can  observe  rocky  places  where  the 
plant  formation  represents  different  stages  in  its  evolution.     On 
rocky  shores,  whether  of  the  precipitous  bluff  type,  or  sloping  rock, 
smooth  or  creviced,  of  large  or  small  boulders,  the  plant  formations 
are  often  modified  greatly  by  the  proximity  to  water,  in  comparison 
with  those  of  the  interior;   for  example,  the  effect  of  surf  action 
or  spray.     The  most  striking  difference  is  perhaps  seen  in  the 
tendency  to  a  zonal  arrangement  of  formations  on  the  gradual 
slopes,  whether  on  seashore,  lake,  or  river,  but  on  the  irregular 
surface-rock  shore  the  distribution  is  azonal. 

1094.  Open  formations  in  rocky  places. — First,  rock  lichens 
and  algae  grow  on  the  bare  rock.     If  there  are  no  crevices  in 

600 


VEGETATION  OF  ROCKY  PLACES.  6oi 

the  rock  this  stage  may  continue  for  ages  unless  the  rock  is  so 
situated  that  the  disintegrated  plant  remains  and  the  weatherings 
of  the  rock  are  not  washed  away.  Umbilicaria,  a  dark-colored 
lichen,  circular  in  form,  often  10-2 $cm  broad,  and  attached 
to  the  smooth  rock  by  a  central  "umbilicus,"  is  a  good  example. 
This  is  sometimes  very  common  on  smooth,  perpendicular  rocks 
by  lake  shores,  or  on  boulders  in  moist  woods  or  regions.  Par- 
melia  is  also  a  common  lichen  clinging  closely  to  the  smooth 
surface  of  rocks.  So  there  are  here  Umbilicaria  formations, 
Parmelia  formations,  Theloschistes  formations,  etc. 

1095.  Lichens  are  among  the  pioneers  in  soil-making.— 
The  habit  which  many  lichens  have  of  flourishing  on  the  bare 
rocks  fits  them  to  be  among  the  pioneers  in  the  formation  of  soil 
in  rocky  regions  \vhich  have  recently  become  bared  of  ice  or 
snow.  The  retreat  of  glaciers  from  peaks  long  scoured  by  ice, 
cr  the  unloading  cf  broken  rocks  along  its  melting  edge,  exposes 
the  rocks  to  the  weathering  action  of  the  different  elements.  Now 
the  lichens  lay  hold  on  them  and  invest  them  with  fantastic 
figures  of  varied  color.  Disintegrating  rock,  debris  of  plants 
and  animals,  join  to  form  the  virgin  soil.  Certain  of  the  blue- 
green  algae,  as  well  as  some  of  the  mosses,  are  able  to  gain  a 
foothold  on  rocks  and  assist  in  this  process  of  soil  formation. 
A  view  of  rocks  thrown  down  by  the  melting  and  retreating  edge 
of  a  glacier  in  Greenland  is  shown  in  fig.  525.  These  rocks  at 
the  time  the  photograph  was  taken  had  no  plant  life  on  them. 
At  other  places  in  the  vicinity  of  this  glacier,  rocks  longer  un- 
covered by  ice  were  being  covered  by  plant  life.  One  of  the 
Greenland  rock  lichens  is  shown  in  fig.  524, 

1095a.  Succession  of  plants  as  soil  is  formed. — If  the  rock  is 
creviced,  these  rudimentary  soil  ingredients  collect  in  the  crevices 
and  afford  a  place  for  mosses  or  the  smaller  seed  plants,  especially 
those  which  form  low,  compact,  cushion-shaped  masses.  Examples 
of  crevice  plants  are,  lichens  like  Cladonia,  with  several  species; 
mosses  like  Hedwigia,  Andraca,  though  these  also  grow  on  smooth 
rock;  ferns  like  Polypodium,  Dryopteris,  Pellaca,  some  species 
of  Asplenium;  herbs  like  the  harebell  (Campanula  rotundifolia), 


602 


RELATION   TO   ENVIRONMENT. 


bluets  (Houstonia  purpurea),  alum-root  (Heuchera  americana), 
Arenaria  stricta;  grasses  like  Agrostis  hiemalis,  etc.  Shrubs  like 
Cornus,  Spiraea,  some  of  the  cedars,  etc.,  while  trees  like  the 
white  pine  (Pinus  strobus),  also  Pinus  divaricatus,  oaks  (Quer- 


Fig.  524. 
Rock  lichen  (umbilicaria)  from  Greenland. 


cus  macrocarpa),  ash  (Fraxnus  americana),,  and  trembling  pop- 
lar (Populus  tremuloides)  occur. 

1096.  Transition  of  open  formations  into  close  ones.— This 
vegetation  together  with  greater  accumulations  of  fine  rock  ingre- 
dients provides  soil  in  the  crevices  where  plants  with  greater 
stem  development  may  gain  a  foothold  in  the  crevices.  These 


VEGETATION  OF  ROCKY  PLACES. 


603 


plants  stand  farther  from  the  substratum  and  gain  an  advantage 
in  light  relation  above  the  earlier  ones.  In  case  the  creviced  rock 
is  where  soil  may  be  washed  over  the  rock  occasionally  in  high 
flood,  an  older  type  of  plant  formation  may  begin  at  once,  since 


Fig.  525- 

Edge  of  glacier  in  Greenland,  showing  freshly  deposited  rocks.     (From  Prof. 
R.  S.  Tarr.) 

the  crevices  are  apt  to  be  filled  with  soil  left  by  the  flood. 
Eventually  the  accumulation  of  soil  may  be  so  great  as  to  encour- 
age a  close  or  climatic  formation. 

1097.  Retention  of  made  soil.— In  the  struggle  of  plants  for 
existence,  there  are  a  number  of  species  which  stand  ready  to 


RELATION    TO   ENVIRONMENT. 


rush  in  where  new  opportunities  present  themselves  by  changed 
conditions  or  by  newly  made  soil.  The  permanent  drainage  of 
ponds  or  marshes  brings  changed  conditions,  and  the  flora  there 
undergoes  remarkable  transformations.  The  deposits  of  the 
washings  of  streams  in  protected  places  along  the  shores,  or  at 
their  mouths,  where  deltas  or  lateral  plateaus  are  made  by  the 
accumulations  of  soil  scoured  off  the  banks  of  the  stream,  or 


Fig.  526. 
Sycamores,  grasses,  and  weeds,  starting  in  crevices  on  a  rock  bed,  New  York. 

washed  off  the  fields  during  rains,  make  new  ground.  With  such 
banks  of  newly  made  ground  are  deposited  seeds  carried  along 
with  the  soil,  or  dropped  there  by  the  wind,  by  birds,  or  other 
agencies  of  seed  distribution. 

Plants  vary  greatly  in  their  capacity  to  occupy  and  hold  new 
territory  and  to  invade  occupied  territory  and  displace  the  inhabit- 
ants. The  first  plants  to  get  a  foothold  are  not  always  the  ones 
to  endure  longest,  and  a  royal  struggle  takes  place  during  years 


VEGETATION  OF  ROCKY  PLACES.  605 

for  supremacy.  The  most  aggressive  species  win  out  in  the  end. 
But  it  must  be  understood  that  with  this  aggressiveness  there 
must  also  be  adaptability  to  the  conditions  of  environment,  for 
a  plant  which  might  succeed  under  one  set  of  conditions  might 
fail  ignominiously  under  another  set  of  conditions.  So,  too, 
certain  plants  may  be  especially  adapted  to  a  certain  set  of  con- 
ditions, but  may  have  the  effect  of  so  changing  the  conditions  by 
building  up  soil  or  the  accumulation  of  humus  that  other  aggres- 
sive species  may  now  enter  and  dispossess  them.  In  this  way  the 
plant  formations  build  one  upon  another,  gradually  approaching 
the  climax  type,  which  remains  permanent  so  long  as  conditions 
are  unchanged,  but  the  climax  type  itself  often  goes  down  in  the 
event  of  the  action  of  great  physiographic,  climatic,  physical 
changes,  or  biological  factors. 

In  the  past  little  attention  has  been  given  to  the  development  or  evolu- 
tion of  the  climax  vegetation  types  from  the  embryonic  ones.  Treub,  in 
1888,  studied  the  rehabilitation  of  plants  of  the  volcano  Krakatau  three 
years  after  the  mountain  was  covered  with  glowing  lava  (Bimstein)  and 
volcanic  ash.  The  dry  rock  and  ash  was  first  covered  with  microscopic 
blue-green  algae  (Cyanophyceae),  which  formed  a  soil  for  ferns  of  which 
in  three  years  there  were  eleven  species,  besides  scatte-ed  seed -plants. 
Schimper  studied  the  vegetation  of  the  volcano  Gunttir  in  West  Java,  which 
at  the  time  of  the  eruption  in  1843  was  covered  with  glowing  volcanic  matter. 
The  vegetation  was  still  quite  open  and  in  places  thin.  There  were  no  trees, 
while  shrubs  'and  herbs  were  present  as  well  as  numerous  ferns,  but  not 
forming  the  chief  mass  of  vegetation  as  at  Krakatau.  A  remarkable 
thing  was  the  fact  that  many  species  which  in  the  forests  were  epiphytes, 
growing  near  the  forest  top  where  they  could  obtain  light,  were  here  grow- 
ing on  the  rocks,  where  in  the  open  formation  light  was  abundant,  as 
many  ferns,  orchids,  and  shrubs  like  Rhodendron  javanicum,  and  Ne- 
penthes with  its  pitchers  containing  water  and  numerous  insects.  Flau- 
hault  and  Combres  have  traced  the  growth  of  the  vegetation  in  the  sandy 
and  dune  lowlands  of  Camargue  in  the  delta  of  the  Rhine,  from  the  naked 
ground  formed  in  floods,  through  the  open,  and  later  to  the  close  forma- 
tions (1894).  Vegetation  established  here  and  there  on  the  beach  during 
the  winter  is  swept  by  the  ocean  storms  and  torn  away.  But  occasionally 
tufts  hold  their  ground  over  winter.  These  increase,  catch  humus,  afford 
a  foothold  for  other  salt-loving  plants;  a  small  dune  is  formed;  this  grows; 
the  rhizomes  of  grasses  and  shrubs  binding  the  soil  and  holding  the  life 
of  the  plant  through  the  winter  period.  As  the  dune  becomes  larger  it 


606  RELATION   TO   ENVIRONMENT. 

moves  above  and  beyond  the  wave  action  of  the  salt  water.  Rains  change 
the  salt  moisture  from  salt  to  fresh  and  the  vegetation  changes  from  halo- 
phytes  to  psammophytes,  the  latter  being  grasses  adapted  to  sandy  soil 
with  fresh-water  infiltration.  By  wind  action  sand  is  carried  farther  from 
the  shore,  and  dunes  of  varying  size  and  age  are  formed  parallel  with  the 
shore.  The  younger  ones  near  the  shore  have  the  open  formations,  while 
farther  inland  the  older  ones  begin  to  take  on  a  closed  formation  with  trees 
and  shrubs  more  abundant,  a  sign  that  the  climax  type  is  being  reached. 
MacMillan  in  1898  has  used  the  same  method  with  excellent  results  in 
his  study  of  the  distribution  of  plants  on  the  shores  of  the  Lake  of  the 
Woods  in  northern  Minnesota.  Later  Cowles  (1898)  has  applied  the 
same  principle  in  the  study  of  the  Physiographic  Ecology  of  Chicago,  and 
in  his  studies  of  the  sand-dunes  of  Lake  Michigan.  Whitford  (1898), 
Genetic  Development  of  the  Forests  of  Northern  Michigan ;  Kearney,  Veger 
tation  of  the  Dismal  Swamp;  Ganong  (1903),  The  Vegetation  of  the  Bay 
of  Fundy  Salt  and  Diked  Marshes;  Fink  (1903),  Some  Talus  Cladonia 
Formations,  and  others. 

II.  Vegetation  of  Swamps  and  Moors. 

1098.  Mud  swamp  or  reed  societies. — The  flora  of  some  soil 
shores  is  very  closely  related  to  that  of  the  mud  swamp.  The 
ground  is  rich  in  nitrogenous  plant-food  from  well-decayed  vege- 
tation matter  mixed  with  the  soil.  The  characteristic  plants  are 
bullrushes,  reed-grasses,  cattail-flag,  sparganium,  sedges,  arrow- 
leaf,  and  often  pondweeds  and  pond-lilies.  These  plants  grow 
in  rather  shallow  water  of  varying  depth,  and  thus  where  the 
ground  is  sloping  often  show  the  zonal  arrangement  with  very 
distinct  formations  (as  Typha  formation).  The  reeds  and  bull- 
rushes  usually  stand  out  with  the  greater  part  of  the  plant  above 
the  water,  and  while  they  are  by  some  called  hygrophytes,  or 
hydrophytes,  the  aerial  parts  are  of  such  a  structure  as  will  retard 
transpiration.  This  would  seem  necessary  since  so  large  a  part 
of  the  plant  is  exposed  to  sun  and  wind,  while  the  roots  are  im- 
mersed in  water  and  absorption  is  thus  lessened.  Where  they 
stand  in  this  relation  to  water  they  are  often  called  semiaquatic 
plants.  The  water-lilies,  pondweeds,  arrow-leaf,  etc.,  are  true 
hydrophytes.  With  the  accumulation  of  vegetation  year  after 
year  the  water  becomes  shallower  in  the  mud-swamp,  until  the 


VEGETATION   OF  ROCKY  PLACES.  60? 

ground  is  built  up  to  water-level,  when  it  passes  into  the  type  of 
the  meadow  swamp. 

1099.  Meadow-swamp  societies,  or  meadows.— These  repre- 
sent a  progressed  stage  of  the  mud  or  reed  swamp.     Grasses  and 
sedges  suited  to  growing  in  wet  soil  or  in  swales  follow  the  reed- 
grass   and   scirpus,    forming  meadow-like   expanses.     Here   and 
there  one  or  more  species  of  grass  or  other  herb  would  dominate 
and  make  the  formation,  as  Cyperus  formation,  Carex  formation, 
or  the  true  grasses,  according  to  the  dominant  species.     A  lux- 
uriant vegetation  is  usually  formed  because  the  soil  is  black  and 
rich  with  nitrogenous  plant-food,  and  the  low  situation  of  the 
ground  assures  an  abundance  of  ground- water.     These  are  the 
true  meadows,  though  the  name  is  given  popularly  to  any  meadow- 
like  expanse  on  higher  ground  where  grasses  are  the  dominant 
vegetation  forms,  whether  in  waste  places  or  cultivated  areas. 
See  also  meadow-moors  in  the  following  paragraph. 

1100.  Peat-moor  societies,  or  bogs  (also  called  muskeag). — The 
ground  of  the  peat-moor  or  peat-bog  is  largely  composed  of  peat 
characterized    by  an   abundance    of  vegetable    matter.     In   the 
moor  only  partial  decay  of  vegetation  takes  place.     This  is  due 
to  an  abundance  of  water,  which  accounts  for  the  small  amount  of 
oxygen,  the  absence  of  the  kinds  of  bacteria  and  fungi  which 
reduce  vegetation  to  humus  and  finally  to  plant-food.     There 
is  produced  then  an  abundance  of  humus  acid  in  the  form  of 
humates.      Two   kinds  of  peat-moors  are   recognized  by  some, 
characterized  by  the  presence  or  absence  of  lime.     The  "high" 
moors  have  an  abundance  of  free  humus,  but  lime  is  lacking, 
while  in  the  so-called  meadow-moors,  which  do  not  have  such  a 
thick  ground  formation,  the  humus  acid  is  combined  with  lime. 
Both  of  these  kinds  of  moors  are  poor  in   mineral  substances 
because,  being  built    up  of   decaying   vegetation    in    the  water, 
the  decay  is  only  partial,  " ground"  is  built  up  rapidly  upon  the 
bottom  of  the  pond,  and  rock-soil  constituents  are  largely  ex- 
cluded.    They  are  rich  in  nitrogenous  matter,  but  this  is  com- 
bined with  humus  in  the  form  of  humified  albuminous  bodies. 
It  is  thus  not  readily  available  for  plant-food.     This,  together 


608  DELATION   TO   ENVIRONMENT. 

with  the  fact  that  the  humus  acid  present  in  the  moor  retards 
absorption,  gives  a  very  characteristic  aspect  to  the  vegetation 
of  the  moors.  The  vegetation  is  more  or  less  xerophytic.  While 
some  plants  which  grow  on  higher  ground  are  found  in  moors, 

still  there  are  many  plants  which  are 
characteristic  of  the  moors.  Some  of 
these  plants  are  found  in  both  the  high 
moor  and  meadow-moor,  but  there  are 
a  few  which  are  characteristic  of  each 
kind,  so  that  the  meadow-moor  con- 
tains many  species  which  are  not 
found  in  the  high  moor. 

The  meadow-moors  have  grasses 
or  sedges  as  the  dominant  vegetation, 
so  that  there  are  "meadows,"  or 
meadow-like  expanses  of  grasses. 
These  would  be  classed  technically 
with  meadows,  but  differ  from  the 
other  types,  where  there  is  more  true 
soil  and  vegetation  thoroughly  decayed. 
The  high  moors  have  been  built  up 
principally  by  growth  of  the  peat-moss, 
or  sphagnum.  The  spongy  character  of 
the  cushions  of  sphagnum  enables  it  to 
lift  water  up  from  below  so  that  the 
lower  parts  are  partially  decayed  and 
yet  the  upper  parts  are  abundantly 
supplied  with  moisture.  The  struc- 
ture of  the  plant  is  especially  favor- 
able for  lifting  up  water.  The  main 
axis  bears  lateral  branches  nearly  at 
right  angles,  but  with  a  graceful  down- 
'Fig  527  ward  sweep  at  the  extremity.  These 

Two  fruiting  plants  of  sphag-  primary  lateral  branches  bear  second- 

num.    (From  Kerner-and  Oliver.)  . 

ary    branches,    which    arise,    usually 
several,  from  near  the  point  of  attachment  to  the  main  axis. 


VEGETATION  OF  ROCKY  PLACES.  609 

They  hang  downward,  overlap  on  those  below,  and  completely 
cover  the  main  axis  or  stem.  The  leaves  of  sphagnum  are 
peculiarly  adapted  for  the  purpose  of  taking  up  quantities  of 
water.  Not  all  the  cells  of  the  leaf  are  green,  but  alternate 
rows  of  cells  become  broadened,  lose  their  chlorophyll,  and  their 
protoplasm  collapses  on  the  inner  faces  ot  the  cell-walls  in  such  a 
way  as  to  form  thickened  lines,  giving  a  peculiar  sculpturing  effect 
to  them.  Perforations  also  take  place  in  the  walls.  These  empty 
cells  absorb  large  quantities  of  water,  and  by  capillarity  it  is  lifted 
on  from  one  cell  to  another.  These  pendant  branches,  then,  which 
envelop  the  sphagnum  stem,  lift  water  up  from  the  moist  sub- 
stratum to  supply  the  leaves  and  growing  parts  of  the  plant  which 
are  at  the  upper  extremity.  Year  by  year  the  extension  of  the 
sphagnum  increases  slowly  upward  by  growth  of  the  ends  of  the 
individual  plants,  while  the  older  portions  below  die  off,  partly 
disintegrate,  and  pass  over  into  the  increasing  solidity  and  bulk 
of  the  peat.  It  thus  happens  sometimes  that  the  centers  of 
such  basins  or  moors  are  more  elevated  than  the  margins,  be- 
cause here  a  greater  amount  of  water  exists  in  the  depths  which 
is  pumped  up  for  use  by  the  plants  themselves.  This  is  why. 
such  a  formation  is  called  a  "high"  moor. 

Among  the  plants  found  in  moors  are  the  leather-leaf  (Cas- 
sandra), Andromeda  polifolia,  the  cranberry,  Labrador  tea,  etc. 
These  plants  have  rather  small,  thick,  and  firm  leaves  with  a 
thick  cuticle  and  the  under  surface  in  some  species  provided 
with  scales  or  hairs  to  lessen  the  amount  of  transpiration.  An- 
dromeda polifolia  has  narrow  leaves  with  a  thick  cuticle  and 
the  edges  are  inrolled.  The  Labrador  tea  has  small  elliptical 
leaves  with  a  thick  cuticle  and  the  under  surface  covered  with 
a  dense  mat  of  hairs.  The  moors  are  often  found  where  were 
formerly  small  shallow  ponds,  or  are  found  on  the  shores  of 
larger  bodies  of  water.  The  rapid  accumulation  of  vegetable 
matter  where  it  only  partially  decays,  builds  up  the  ground  floor 
to  such  an  extent  as  to  completely  fill  smaller  ponds  or  lakes 
which  are  not  very  deep.  In  the  high  moor  this  ground  is  built 
up  more  rapidly  than  in  the  meadow-moor,  and  eventually,  when 


6lO  RELATION   TO   ENVIRONMENT. 

the  pond  is  filled,  the  ground  formation  in  the  center  becomes 
more  elevated  than  toward  the  margin.  Transeau  (1903)  has 
shown  in  an  interesting  way  how  these  plant  societies  of  peat- 
moors  are  related  to  the  arctic  tundra.  The  evidence  seems  to 
show,  as  earlier  students  have  also  pointed  out,  that  during  the 
glacial  period  these  arctic  plants  moved  southward  in  advance 
of  the  great  ice-sheet.  When  the  glacier  retreated  to  the  north 
many  of  these  plants  were  left  behind.  In  situations  like  the 
present  moors,  where  the  climatic  type  of  vegetation  could  not 
take  possession  of  the  ground  because  of  soil  peculiarities,  these 
arctic  plants  have  retained  possession;  the  very  soil  conditions 
here  which  prevent  the  growth  of  the  forest  favor  the  growth 
of  these  plants.  It  has  long  been  known  that  a  number  of 
the  heaths  and  other  shrubs  growing  in  these  moors  were  very 
similar  to  and  in  a  few  cases  identical  with  certain  species  grow- 
ing in  the  cold  wastes  of  arctic  regions.  For  example,  the  moss 
plant  (Cassiope  hypnoides),  the  four-angled  cassiope  (Cas- 
siope  tetragona),  and  others  extend  from  the  Northern  States  to 
arctic  America. 

1101.  Insectivorous  plants  on  moors. — Most  plants  growing 
in  moors  have  difficulty  in  obtaining  food  because  of  the  small 
amount  of  mineral  substances,  the  unavailable  form  of  much 
of  the  nitrogen,  and  the  interference  with  absorption  due  to 
lack  of  oxygen  and  the  presence  of  humus  acid.  Some  moor 
plants,  however,  are  assisted  in  obtaining  food  because  of  their 
carnivorous  habit.  These  are  the  insectivorous  plants  like  the 
sundews  (Drosera),  the  pitcher  plant  (Sarracenia  purpurea), 
the  butterwort,  or  bog  violet  (Pinguicula  vulgaris),  the  horned 
bladderwort  (Utricularia  cornuta),  etc.  In  the  sundews  there 
are  viscid  glandular  hairs  (fig.  127)  on  which  flies  get  stuck. 
These  hairs  are  sensitive,  they  bend  inward,  bearing  the  fly 
against  the  leaf  so  that  it  folds  over  it,  and  certain  juices  from 
the  leaf  digest  the  insect.  In  the  butterwort  the  flies  are  stuck 
to  the  surface  of  the  sticky  leaf.  In  the  bladderwort,  many 
species  of  which  grow  in  water,  there  are  bladder-like  leaves 
with  a  trap-door  at  the  opening,  so  that  insects  can  easily  swim 


VEGETATION   OF   ROCKY  PLACES.  6ll 

in  but  cannot  get  out.  The  Venus's  fly-trap  (Dionaea  muscipula, 
fig.  126)  on  sandy  coastal  lowlands  of  North  Carolina  is  one  of 
the  most  remarkable  of  the  insectivorous  plants.  When  insects 
alight  on  the  leaf  and  irritate  the  hairs  on  the  surface  the  leaf 
closes  suddenly  and  the  stout  hairs  on  the  edges  fit  in  between 
one  another  like  the  teeth  of  a  steel  trap  and  prevent  the  escape 
of  the  insect,  while  the  surfaces  of  the  leaf  are  gradually  pressed 
tightly  against  it,  and  fluids  exuded  by  the  leaf  digest  the  insect. 

1102.  A  plant  atoll. — In  the  morainic  regions  of  central  New 
York  there  are  some  interesting  and  striking  examples  of  the 
effects  of  plants  on  the  topography  of  small  and  shallow  basins. 
These  formations  sometimes  take  the  shape  of  " atolls,"  though 
plants,  and  not  corals,  are  the  chief  agencies  in  their  gradual  evolu- 
tion. Fig.  484  is  from  a  photograph  of  one  of  these  plant  atolls 
about  fifteen  miles  from  Ithaca,  N.  Y.,  along  the  line  of  the 
E.  C.  &  N.  R.  R.,  near  a  former  flag-station  known  as  Chicago. 
The  basin  here  shown  is  surrounded  by  three  hills,  and  is  formed 
by  the  union  of  their  bases,  thus  forming  a  pond  with  no  outlet. 

Topography  of  the  atoll-moor. — The  entire  basin  was  once  a 
large  pond,  which  has  become  nearly  filled  by  the  growth  of  a 
vegetation  characteristic  of  such  regions.  Now  only  a  small, 
nearly  circular,  central  pond  remains,  while  entirely  around 
the  edge  of  the  earlier  basin  is  a  ditch,  in  many  places  with  from 
30-60  cm  of  water.  There  is  a  broad  zone  of  land  then  lying 
between  the  central  pond  and  the  marginal  ditch.  Just  inside 
of  the  ring  formed  by  the  ditch  is  an  elevated  ring  extending  all 
around,  which  is  higher  than  any  other  part  of  the  atoll.  On  a 
oortion  of  this  ring  grow  certain  grasses  and  carices.  The  soil 
for  some  depth  shows  a  wet  peat  made  up  of  decaying  grasses, 
carices,  and  much  peat-moss  (sphagnum).  In  some  places  one 
element  seems  to  predominate,  and  in  other  cases  another  ele- 
ment. On  some  portions  of  the  outer  ring  are  shrubs  one  to  three 
meters  in  height,  and  occasionally  small  trees  have  gained  a 
foothold. 

Next  inside  of  this  belt  is  a  broad,  level  zone,  with  Carex 
filiformis,  other  carices,  grasses,  with  a  few  dicotyledons.  Inter- 


RELATION    TO   ENVIRONMENT. 


VEGE  TA  T2ON  OF  ROCKY  PL  A  CES.  6 1 3 

mingled  are  various  mosses  and  much  sphagnum.  The  soil 
formation  underneath  contains  remains  of  carices,  grasses,  and 
sphagnum.  This  intermediate  zone  is  not  a  homogeneous  one. 
At  certain  places  are  extensive  areas  in  which  Carex  filiformis 
predominates,  while  in  another  place  another  carex,  or  grasses, 
predominate. 

A  floating  inner  zone. — But  the  innermost  zone,  that  which 
borders  on  the  water,  is  in  a  large  measure  made  up  of  the  leather- 
leaf  shrub,  cassandra,  and  is  quite  homogeneous.  The  dense 
zone  of  this  shrub  gives  the  elevated  appearance  to  the  atoll 
immediately  around  the  central  pond,  and  the  cassandra  is 
nearly  one  meter  in  height,  the  "ground"  being  but  little  above 
the  level  of  the  water.  As  one  approaches  this  zone  the  ground 
yields,  and  by  swinging  up  and  down,  waves  pass  over  a  consider- 
ble  area.  From  this  we  know  that  underneath  the  mat  of  living 
and  recent  vegetation  there  is  water,  or  very  thin  mud,  so  that 
a  portion  of  this  zone  is  "floating." 

The  inner,  or  cassandra,  zone  is  more  unstable,  that  is,  it  is 
all  "afloat,"  though  firmly  anchored  to  the  intermediate  zone. 
The  roots  of  the  shrubs  interlace  throughout  the  zone,  firmly 
anchoring  all  parts  together,  so  that  the  wind  cannot  break  it 
up.  Between  the  tufts  of  cassandra  are  often  numerous  open 
places,  so  that  the  water  or  thin  mud  on  which  the  zone  floats 
reaches  the  surface,  and  one  must  exercise  care  in  walking  to 
prevent  a  disagreeable  plunge.  No  resistance  is  offered  to  a 
pole  two  to  three  meters  long  in  thrusting  it  down  these  holes. 
Grasses,  carices,  mosses,  sphagnum,  and  occasionally  moor-loving 
dicotyledons  occur,  anchored  for  the  most  part  about  the  roots  of 
the  cassandra.  Standing  at  the  inner  margin  of  the  cassandra 
zone,  one  can  see  the  mud,  resembling  a  black  ooze,  formed  of  the 
broken  plant-remains,  which  have  floated  out  from  the  bottom 
of  the  older  formations.  In  some  places  this  lies  very  near  the 
surface,  and  then  certain  aquatic  plants,  like  Bidens  and  others, 
find  a  footing.  Upon  this  black  ooze  the  formation  can  continue 
to  encroach  upon  the  central  pond.  Agitated  by  the  wind,  more 
and  more  of  the  ooze  passes  outward,  so  that  in  time  there  is  a 


614 


RELATION    TO   ENVIRONMENT. 


VEGETATION   OF  ROCKY  PLACES.  615 

likelihood  that  the  pond  will  cease  to  exist,  yielding,  as  it  has 
in  other  places,  the  right  of  possession  to  the  encroaching  vege- 
tation. 

How  was  the  atoll  formed? — In  the  early  formation  of  the 
atoll  it  is  possible  that  certain  of  the  water-loving  carices  and 
grasses  began  to  grow  some  distance  (three  or  four  meters) 
from  the  shore,  where  the  water  was  of  a  depth  suited  to  their 
habit.  The  stools  of  these  plants  gradually  came  nearer  the 
surface  of  the  water.  As  they  approach  the  surface  other  plants, 
not  so  strong-rooted,  like  mosses,  sphagnum,  etc.,  find  anchorage, 
and  are  also  protected  to  some  extent  from  the  direct  rays  of 
sunlight.  Partial  disintegration  of  the  dead  plant  parts,  which, 
mingling  with  the  soil,  gradually  fills  on  the  inside  of  the  zone, 
so  that  the  depth  of  the  water  there  becomes  less.  Now  the 
zone  of  the  carices  can  be  extended  inward. 

The  continued  growth  of  the  sphagnum  and  the  dying  away 
of  the  lower  part  of  the  plant  add  to  the  bulk  of  the  plant-remains 
in  the  zone,  and  finally  quite  a  firm  ground  is  formed,  shutting 
off  the  shallow  water  near  the  shore  from  the  deeper  water  of  the 
pond.  As  time  goes  on  other  plants  enter  and  complicate  the 
formation,  and  even  make  new  ones,  as  when  the  cassandra 
takes  possession. 

The  original  pond  here  was  rather  oblong,  and  one  end  possi- 
bly much  shallower  than  the  other,  so  that  it  filled  in  much  more 
rapidly,  leaving  the  central  pond  at  the  east  end.  Over  a  por- 
tion of  the  west  end  there  is  an  extensive  cassandra  formation, 
with  some  ledum  (Labrador  tea) ,  but  separated  from  the  circular 
cassandra  zone  by  an  intermediate  zone.  In  this  end-cassandra 
formation  other  shrubs,  and  white  pines  five  to  fifteen  years  old, 
are  gaining  a  foothold,  and  in  a  quarter  of  a  century  or  more, 
if  left  undisturbed,  one  may  expect  considerable  changes  in  the 
flora  of  this  atoll. 

The  ditch  on  the  margin  of  the  atoll-moor  was  probably  formed 
because  of  the  shade  offered  by  the  forest  on  the  banks.  On 
the  side  where  the  original  forest  still  stands  the  ditch  is  deeper, 
and  where  it  is  heavily  shaded  no  vegetation  is  present  close  to 


6l6  RELATION    TO   ENVIRONMENT. 

the  bank  except  some  algae  and  liverworts.  On  the  sides  where 
the  forest  has  been  cleared  off  swale-grasses  are  growing  in  the 
ditch  or  marginal  depression  and  ground  is  being  slowly  built  up. 
1103.  Heaths. — Heaths  or  heath-moors  are  plant  societies 
where  heaths  are  the  dominant  vegetation.  Examples  of  heaths 
are  huckleberries  and  bearberries,  cranberries  (Vaccinium 
species),  but  especially  members  of  the  Ericaceae,  like  wild  rose- 
mary (Andromeda),  dwarf  cassandra  (Chamaedaphne  =  Cassan- 
dra), heather  (Calluna  vulgaris),  etc.  These  usually  occur  in 
sphagnum-moors  (see  sphagnum-moors),  but  sometimes  heath 


Fig.  530. 

Heather  formation  on  sand  in  crevices  of  rock.  Heather  (Calluna  vulgaris)  in 
the  foreground  and  in  rock  crevices  on  the  left.  At  the  right  a  few  dwarfed, 
stunted  trees  of  Pinus  sylvestris  bent  to  one  side  by  wind.  On  rocky  hills,  coast 
of  Sweden,  Botanic  Garden,  Gothenburg.  (Photograph  by  the  author.) 

formations  are  on  sandy  ground,  which  is  more  elevated  and  dry, 
especially  the  heather  (Calluna  vulgaris).  The  heather  forms 
extensive  heaths  in  northwestern  Europe  either  in  moors  or  on 
dry,  sandy  ground.  It  also  occurs  in  northeastern  North  America, 
but  is  rather  local. 

1103a.  Spruce  and  tamarack  swamps. — The  black  spruce  and 
the  larch  or  tamarack  often  encroach  on  the  peat-moors,  heaths, 
or  muskeags,  and  make  distinct  formations.  The  trees  in  this 


VEGETATION  OF  ROCKY  PLACES. 


6I7 


situation   are   usually   of   slow   growth.     The   under   vegetation 
consists  of  shrubs,  herbs,  and  mosses  like  those  on  the  moors 


Fig-  53i- 

Dying  black  spruce  in  moor.      Note   the  abundance  of  cotton-grass  (Eriopho- 
rum).      (Photograph  by  the  author.) 

described ,  in  paragraphs  1090-1093.  In  open  places,  or  in 
moors  where  the  spruce  is  dying  because  of  fires  or  floods,  the 
cotton-grass  is  often  abundant,  as  shown  in  fig.  531.  This  grass 
also  occurs  on  other  moors. 

1104.  Cane-swamp  societies. — These     are    frequent    in    the 
Southern  States  in  low  ground  along  streams,  and  are  formed 
by  a  dense  growth  of  the  cane,  Arundinaria. 

1105.  Salt-marsh  societies. — These  are  formed  along  the  salt 
shores  of  the  ocean  or  of  salt  lakes,  where  the  gradient  of  the 
shore  is  low  and  the  soil  is  nitrophytic.     The  water  is  brackish 
and  varies  in  its  salt  content  according  to  the  relation  of  the 
marsh  to  the  sea  and  to  the  run-off  from  the  land.     The  seed 
plants  are  rooted  in  the  soil,  which  is  either  very  wet  with  the 
brackish  water,  or  entirely  submerged,  and  the  plants  also  more 


6i8 


RELATION   TO  ENVIRONMENT. 


or  less  submerged.  With  many  of  these  plants  the  upper  parts 
are  above  the  water.  Because  of  the  large  salt  content  in  the 
water  the  plants  absorb  it  with  difficulty.  The  aerial  parts  then 
are  provided  with  leaves  and  stems  which  retard  transpiration. 
They  are  thus  xerophytic  in  structure  and  habit,  but  are  often 
called  halophytes  because  of  their  adaptation  to  a  large'  salt  con- 
tent in  the  salt  water.  A  similar  flora  is  found  around  salt 
springs.  For  example,  the  maritime  ruppia  (Ruppia  maritima), 
a  plant  found  in  brackish  water  along  the  seacoast,  occurs  in 
the  water  near  salt  springs  in  Onondaga  County,  New  York, 
and  also  in  "alkaline  basins  in  the  West,  while  Salicornia,  etc., 
occur  on  the  ground  in  the  same  regions.  Characteristic  salt 
marshes  are  the  meadows  with  marsh-grasses.  The  mangrove 


Wm 


.    Fig.  532. 

Plants  inarching  into  the  sea.     They  have  advanced  from  the  trees  at  the  left 
in  about  two  hundred  years.     Meadow  in  salt  marsh. 

swamp  is  also  a  characteristic  one,  but  this  is  treated  of  in  forest 
societies.     Ganong  in  an  important  paper  has  shown  how  much 


VEGE TA  TION  OF  ROCKY  PLA CES.  6 1 9 

of  the  area  covered  by  the  salt  marshes  of  the  Bay  of  Fundy  has 
been  converted  into  arable  land,  especially  for  the  growth  of  hay. 
The  farmers  in  that  section  "dyke"  the  marshes  to  prevent  their 
being  flooded  during  high  tide.  Many  of  the  true  salt-marsh 
plant  formations,  as  well  as  the  conditions  of  environment,  are 
discussed.  One  of  the  most  characteristic  halophytes  of  the  salt 
marshes  here  is  the  sedge  spartina  (S.  stricta  glabra).  It  grows 
on  the  shore  down  to  the  water's  edge  along  the  open  ocean,  and 
here  the  plants  are  low  and  stunted,  since  they  are  subject  to 
the  strong  salt  water  during  tide.  It  is  also  one  of  the  characteris- 
tic plants  forming  meadows  in  the  brackish  waters,  and  here  it  is 
more  luxuriant.  It  possesses  true  xerophytic  structures,  propa- 
gates chiefly  by  subterranean  shoots,  and  the  stems  and  leaves 
have  ample  air-spaces.  The  abundance  of  air  in  the  plant  enables 
it  to  endure  prolonged  and  frequent  inundation  by  the  tides. 
Ganong  has  found  by  experiment  that  the  root-hairs  of  a  number 
of  seedlings  of  these  salt-marsh  plants  resist  plasmolysis  when 
immersed  in  quite  strong  saline  solutions,  and  this  probably 
explains  why  it  is  these  plants  are  able  to  grow  in  soil  and  water 
of  such  salt  concentration. 

1106.  Shores  of  marl  ponds. — On  the  shores  of  marl  ponds 
the  soil  is  calcareous,  i.e.,  it  contains  large  quantities  of  lime  in 
the  form  of  carbonate  of  lime,  mixed  with  sand  and  clay  in  vari- 
able proportions  in  different  localities.  These  shores  often  furnish 
a  characteristic  vegetation  which  is  usually  xerophytic.  On  the 
shores  of  marl  ponds  in  New  York  the  shrubby  cinquefoil  (Poten- 
tilla  f ruticosa  =  Dasiphora  fruticosa)  is  often  one  of  the  common 
formations.  The  usual  habitat  for  this  species  is  in  swamps  and 
rocky  places  from  Labrador  to  Greenland  and  Alaska.  (See 
marl  ponds  in  Chapter  LVI.) 


CHAPTER  LVI. 

AQUATIC    PLANT    SOCIETIES. 

I.  General  Considerations. 

IN  this  chapter  are  treated  the  vegetation  forms  which  are  for 
the  most  part  submerged.  Some  float  on  the  water  with  their 
upper  surface  exposed.  In  others  the  leaves  float  on  the  water, 
while  in  still  others  the  leaves  may  be  lifted  considerably  above 
the  surface.  They  differ  from  the  plants  of  swamp  societies  in 
that  the  plants  of  the  latter  have  all  or  a  large  part  of  their  body 
out  of  the  water,  and  are  usually  supplied  with  mechanical  tissue 
for  self-support.  (These  semi-immersed  plants  are  sometimes 
called  semi-aquatics.) 

1107.  General  characters  of  aquatic  plants  (see  also  Chapter 
XLVII,  Hydrophytic  structures). — A  typical  aquatic  plant  has 
at  best  only  a  slight  development  of  mechanical  tissue;  it  is  sup- 
ported by  the  water;   it  is  provided  with  air  by  large  air-spaces 
throughout  the  tissue;    all  or  nearly  all  parts  being  surrounded 
by  water,  absorption  takes  place  directly  and  there  is  little  or  no 
development  of  root-hairs,   and  only  a  feeble  development  of 
fibrovascular  tissue;  where  roots  are  developed  they  serve  chiefly 
as  holdfasts.     Water-plant  societies  grade  into  swamp  societies 
and  these  into  the  vegetation  of  soil  shores.     In  fact  all  three 
types  may  be  present  in  the  same  pond  or  lake  or  shore,  shallow 
water,  or  deep-water  vegetation. 

1108.  Two  general  divisions  of  aquatic  plants. — In  studying 
plant  societies  growing  in  water  it  is  convenient  to  divide  them 

—       -  6  20 


AQUATIC   VEGETATION.  62 1 

into  two  groups  which  correspond  with  the  divisions:  hydro- 
phytes,  which  grow  in  fresh-water  streams,  lakes,  ponds,  etc.; 
and  halophytes,  or  those  which  grow  in  the  ocean  or  in  salt  lakes. 
The  fresh-water  plants  are  sometimes  called  limnetic,  and  the 
marine  forms  pelagic.  In  both  the  limnetic  and  pelagic  floras 
there  are  plants  which  are  fixed  to  some  place  of  support  (to 
the  rocks,  lithophytes,  as  in  case  of  pelagic  forms;  to  the  soil,  as 
in  case  of  most  limnetic  forms;  while  algae,  etc.,  attached  *o 
other  plants  are  epiphytes),  while  others  are  free-floating  or 
swimming.* 

1 109.  Different  regions  of  light  in  deep  water. — Aquatic  plants 
are  distributed  at  different  depths  in  the  water,  and  it  is  sur- 
prising the  depth  at  which  some  can  live.  It  is  obvious  that 
plants  located  at  different  depths  will  have  different  light  rela- 
tions, those  near  the  surface  being  well  lighted,  while  those  lower 
down  will  receive  light  of  diminished  intensity.  Light  is  the 
controlling  factor,  and  three  regions  are  recognized,  ist.  The 
bright-light  region,  or  photic  region,  in  which  the  light  intensity 
is  favorable  for  the  normal  development  of  the  larger  plants, 
(macrophytes).  It  is  the  region  also  of  most  of  the  microphytes 
which  have  photosynthesis,  especially  the  green  algae.  2d.  The 
dimly-lighted  region,  or  dysphotic  region,  where  most  of  the 
macrophytes  reach  only  a  stunted  growth  or  fail,  and  where  a 


*  Schimper  uses  the  term  Benthos  or  benthonic  (0evQoS=  depths)  for 
those  forms  which  are  fixed.  Plankton  is  the  term  applied  to  the  free- 
swimming  or  floating  forms,  but  perhaps  its  best  expression  is  now  for 
the  swimming  microscopic  plant  and  animal  forms  of  deep  water.  Plank- 
ton was  first  used  to  signify  pelagic  animals.  The  best  examples  of  plant 
plankton  are  found  in  the  Protococcoideae,  floating  and  swimming  green 
algas,  as  Volvox,  Pandorina,  Eudorina,  Chlamydomonas,  etc.,  the  desmids, 
the  blue-green  algae,  the  Peridineae,  and  the  diatoms  especially.  The 
diatoms  have  a  siliceous  external  skeleton.  They  occur  in  great  numbers 
in  fresh  water,  but  in  vastly  greater  numbers  in  the  ocean.  In  geologic 
times  they  were  so  abundant  for  long  periods  that  their  skeletons  have  built 
up  great  rock  formations.  Hemiplankton  is  a  term  applied  to  those  plants 
floating  and  swimming  in  the  shallow  water  of  the  coast  or  in  the  shallow 
waters  of  inland  lakes  and  ponds,  where  they  are  mixed  with  benthonic  forms. 


622  RELATION   TO  ENVIRONMENT. 

few  photosynthetic  microphytes,  especially  diatoms,  grow.     3d. 
The   dark   region,    or   aphotic  region,  only   occupied  by  those 


Fig.  533<*. 

Macrophytes  in  the  upper  zone  of  the  photic  region.  Ascophyllum  and  Fucui 
at  low  tide,  Hunter's  Island,  New  York  City.  (Photograph  by  M.  A.  Howe.) 

organisms  not    capable  of   photosynthesis  (certain   bacteria  for 
example).* 

1110.  Concentration  of  salt  water.— The  degree  of  concentra- 
tion of  salt  solutions  in  water  affects  the  distribution  of  plants. 
The  concentration  of  salt  water  varies  in  the  different  inland  salt 
lakes  and  seas  because  of  the  varying  rapidity  of  evaporation 
and  the  different  proportions  of  fresh  water  draining  into  them. 
The  concentration  of  the  salt  water  of  inland  seas  is  different 
from  that  of  the  ocean,  and  here  it  usually  diminishes  from  the 
open  sea  toward  the  coast.  The  greatest  salt  content,  according 
to  Schimper,  is  found  in  the  Red  Sea  |  (4.3  per  cent),  in  conse- 
quence of  rapid  evaporation  and  the  small  amount  of  fresh  water 
flowing  into  it,  while  in  the  Baltic  Sea  it  is  as  low  as  i  per  cent. 
In  the  ocean  the  content  of  mineral  matter  is  about  3.5  per  cent, 
of  common  salt  about  2.6  per  cent,  and  it  is  greater  in  tropical 


*  In  the  Gulf  of  Naples  living  bacteria  have  been  found  at  a  depth  of 
250-1  loom  (=800-3500  ft.). 

f  The  color  of  the  Red  Sea  is  due  to  the  red  schimmer  given  it  by  the 
swimming  alga  Trichodesmium  erythraeum,  one  of  the  Cyanophyceas. 


AQUATIC   VEGETATION.  623 

than  in  arctic  or  antarctic  regions.  At  the  mouth  of  rivers  and 
streams,  in  salt  marshes,  and  in  some  inland  salt  seas  which 
have  a  large  influx  of  fresh  water,  it  is  "brackish,"  i.e.,  slightly 
saline. 

lllOa.  Movement  of  water  also  affects  the  form  and  character 
of  aquatic  plants.  In  quiet  fresh  water  the  plants  are  different 
from  those  in  streams.  Ebb  and  flow  of  tide  show  their  effect 
on  pelagic  forms.  The  physical  condition  of  the  substratum, 
whether  rock  or  soil,  affects  the  benthonic  vegetation.  Aside 
from  the  effect  of  salt  water,  the  flora  of  fresh  waters  is  in- 
fluenced accordingly  as  it  is  rich  or  poor  in  calcium  carbonate. 

lllOb.  Temperature  exercises  considerable  influence  on  the 
distribution  of  water  plants,  but  is  not  so  important  a  factor  as 
it  is  on  land  because  it  is  more  equable.  Most  of  the  perennial 
pelagic  algae  show  no  period  of  rest;  usually  the  summer  is  the 
growing  period  and  winter  the  fruiting  period,  though  there 
are  a  number  of  exceptions  to  this.  A  greater  difference  is 
manifest  in  the  inland  lakes  and  ponds,  especially  in  the  cool 
temperate  regions,  where  the  formation  of  ice  interrupts  the 
growth,  the  perennial  benthonic  forms  passing  through  a  period 
of  rest  for  their  shoots,  and  the  annuals  and  plankton  passing 
the  period  through  seeds,  spores,  hormogones,  akinetes,  or  re- 
sistant vegetation  parts.  Many  bacteria  and  some  algae  will 
live  enclosed  in  ice  for  considerable  periods.  Certain  benthonic 
algae  (Lemanea)  in  fresh-water  streams  pass  both  the  growing 
and  reproductive  period  in  winter  often  under  ice,  and  rest 
during  the  summer  period.  Warm  currents  exercise  an  in- 
fluence on  the  distribution  of  pelagic  algae,  but  not  so  markedly 
as  they  do  on  land  plants. 

1111.  Inland  salt  ponds  and  lakes. — Since,  in  a  number  of 
the  inland  salt  lakes  and  seas,  the  percentage  of  salt  is  very  high, 
plant  life  is  more  restricted  than  in  the  ocean,  and  in  some  cases 
is  prohibited.  But  at  the  intake  of  fresh-water  streams  the 
salinity  would  be  reduced  and  permit  the  growth  of  certain 
halophytes.  The  vegetation  of  the  saline  waters  of  the  Great 
Salt  Lake  in  Utah  has  not  been  carefully  studied  with  reference 


624  RELATION"   TO   ENVIRONMENT. 

to  environment,  and  yet  we  know  something  of  the  halophytic 
vegetation  of  some  of  the  alkaline  waters  and  of  the  soil  shores 
of  the  lakes  and  ponds  in  the  arid  regions.  See  alkaline  marshes 
and  Bad  Lands  in  Chapter  L.  The  vegetation  in  the  vicinity 
of  the  Great  Salt  Lake  is  similar  to  that  mentioned  here. 

1112.  Marl   ponds. — The  water   in   marl   ponds   contains   a 
large  percentage  of  carbonate  of  lime.     Plant  life  is,  therefore, 
somewhat   restricted.     Certain   species    of    Chara    (one   of   the 
algae),  however,  are  often  very  abundant  in  the  waters  of  marl 
ponds,  and  the  plants  are  very  brittle  because  of  the  large  amount 
of  carbonate  of  lime  in  their  tissues.     (See  shores  of  marl  ponds 
in  Chapter  LV.) 

1113.  Vegetation  of  hot  springs. — The  vegetation    of    hot 
springs  is  remarkable  for  the  high  temperatures  at  which  cer- 
tain bacteria  and  blue-green  algae  can  grow.     In  America  the 
most  notable  instance  is  the  vegetation  of  the  hot  springs  and 
geysers  in  Yellowstone  National  Park.     Certain  filamentous  bac- 
teria grow  in   hot  water,  the  temperature  reaching  as  high  as 
7o°-82°  C.,  or  rarely  as  high  as  89°  C.     In  water  slightly  cooler, 
65°-68°  C.,  or  even  scantily  at  75°-77°  C.,  species  of  the  Cyano- 
phyceae,  like  Phormidium,  occur,  and  in  still  cooler  waters  of  the 
hot  springs  are  found  Anabaena,  Gloeocapsa,  etc.     Some  of  these 
waters  are  rich  in  carbonate  of  lime,  which  some  of  these  plants 
deposit,  forming  curious  and  often  fantastic  figures  in  the  basins. 

II.  Fresh-water,  or  Limnetic,  Plant  Societies. 

1114.  Pond  or  inland-lake  societies. — These  should  be  ob- 
served in  connection  with  swamp  societies  and  the  flora  of  soil 
shores,  since  the  semi-aquatic  plants,  like  the  bulrushes,  cattail- 
flags,  arrow-leaf,  etc.,  growing  in  the  shallow  water  of  the  pond 
or  lake  margin,  are  the  transition  forms  from  the  lowland  or 
swamp  flora  to  the  truly  aquatic  plants.     In  general  several 
zones  can  be  recognized  from  the  shore  lakeward  (see  Chapter 
LV).     The  first  is  a  littoral  zone,  and  includes  the  semi-aquatics 
like  those  mentioned   above,   and   this   is   connected  with   the 


AQUATIC    VEGETATION.  62$ 

strand  flora  by  different  plants,  according  to  the  soil  conditions, 
locality,  and  other  conditions  of  environment  or  factors  of  dis- 
tribution (herbs,  grasses,  etc.).  The  second  zone,  mid  zone,  is 
characterized  for  the  most  part  by  plants  with  floating  leaves 
and  slender  petioles  or  stems,  like  the  water-lilies,  the  floating 
potamogeton  (P.  natans),  the  water-fern  (Marsilea).  It  is 
interesting  to  note  from  year  to  year,  as  the  water  may  be  at 
different  depths,  that  the  perennial  plants  fixed  to  the  bottom 
have  short  or  long  petioles  according  as  the  water  is  shallow  or 
deep.  Some  plants  in  this  zone  are  entirely  immersed,  like 
the  quillwort.  The  latter  sometimes  in  small  ponds  makes 
pure  formations.  In  fact  any  of  the  zones  may  be  pure  or 
mixed,  one  or  several  facies  making  a  formation,  as  in  the  case  of 
land  plants.  The  third  is  a  submerged  zone  and  has  plants  of  the 
true  pondweed  type.  These  occupy  deeper  water,  and  while 
nearly  always  submerged,  their  leaves  are  brought  near  the  surface 
for  light  by  the  elongation  of  their  stems.  These  should  be 
contrasted  with  such  a  plant  as  the  quillwort,  which  does  not 
have  this  power  of  adaptation.  Some  of  the  pondweeds  grow 
where  the  water  is  up  to  6m  (20  ft.)  or  more  deep. 

1114a.  The  three  zones  mentioned  above  are  to  be  taken  in 
a  broad  sense,  and  relate  to:  ist,  littoral  zone,  the  semi-aquatics; 
2d,  mid  zone,  the  forms  with  floating  leaves;  and  3d,  submerged 
zone,  the  completely  submerged  plants.  In  regular  bowl- 
shaped  ponds  or  lakes  there  might  be,  and  usually  are,  several 
plant  formations  arranged  zonally  within  each  of  the  zones 
mentioned  above.  To  take,  for  example,  the  formations  illus- 
trated in  fig.  534.  In  the  littoral  zone  of  semi-aquatics  there 
are  three  zonal  formations:  typha  (i),  the  bulrushes  (2),  and 
arrow-leaf  (3).  In  the  mid  zone  (adjacent  to  this)  the  yellow 
water-lily,  and  potamogetons  with  floating  leaves  (4).  In  the 
submerged  zone  are  two  zonal  formations,  pond-lilies  (5),  and 
bass-weed  =  Chara  (6).  According  to  Magnin,  in  the  small 
lakes  of  Jura  there  are  usually  six  zones,  and  these  correspond 
as  follows  to  the  three  zones  mentioned  above:  ist,  littoral  zone 
of  semi-aquatics,  zone  of  sedges  (i),  zone  of  reed-grasses  (2), 


626  RELATION   TO    ENVIRONMENT. 

zone  of  bulrushes  (3);  2d,  mid  zone,  zone  of  pond-lilies  (4); 
3d,  submerged  zone,  zone  of  pondweeds  (5),  zone  of  bass- 
weed,  Chara  (6).  We  see  then  that  in  different  localities  these 
three  different  zones  may  be  represented  by  different  species, 
but  the  vegetation  types  in  the  different  zones  are  the  same. 

1114b.  The  free-floating  forms,  like  the  duckweed,  riccias, 
Salvinia,  etc.,  are  found  on  the  surface  in  the  first  and  second 
zones,  floating  between  the  stems  and  leaves.  These  are  buoyed 
up  by  large  intercellular  air-spaces.  Here  occur  also  floating 
mats  of  algae,  like  Spirogyra,  Vaucheria,  (Edogonium,  etc., 
which  are  buoyed  up  by  the  bubbles  of  gas  entangled  in  the 
meshes  of  the  mat,  or  algaelike  Cladophora,  which  are  attached 
to  the  reeds  or  bulrushes,  or  Coleochaete,  which  forms  sessile 
disks  on  the  same  supports.  Then  there  are  the  numerous 
free-swimming  green  algae  floating  in  the  meshes  of  thread- 
like alga  mats,  or  swimming  on  the  surface,  or  resting  on  larger 
plants,  or  on  the  bottom  in  shallow  places,  as  well  as  numerous 
blue-green  algae,  diatoms,  bacteria,  and  the  water-mold  fungi. 

1115.  River,  or  fluvial,  plant  societies. — The  plants  which 
grow  in  the  running  water  of  streams  constitute  a  rather  distinct 
type  from  those  in  quiet  water.  Because  of  the  continued 
movement  of  the  water,  sometimes  rapid  or  violent,  the  plants 
are  attached  to  the  rock  or  rooted  well  in  the  ground,  and  have 
flexile  stems,  with  only  slight  leaf  development,  or  the  leaf  may 
not  be  well  differentiated  from  the  stem.  This  type  of  stem 
is  suited  to  the  waving  movements  produced  by  the  flowing 
water.  The  river-weed  (Podostemon)  is  a  good  example  of 
one  of  the  seed-plants  which  has  become  so  changed  in  its  adapta- 
tion to  an  aquatic  life  that  it  strongly  resembles  certain  algae ;  the 
mosses  are  represented  by  Fontinalis,  and  the  algae  by  Clado- 
phora and  Lemanea. 

Where  the  water  is  shallow  or  quiet,  as  in  pools  or  ponds 
having  an  open  connection  with  the  streams,  the  societies  are 
of  the  pool  or  pond  type.  Semi-aquatics  (bulrushes,  reed- 
grasses,  arrow-leaves,  pickerel-weeds,  etc.)  often  develop  along 
the  shore  of  streams  or  in  shallow  water  in  midstreams,  where 


AQUATIC   VEGETATION.  62? 

they  often  catch  debris,  and  eventually  fix  a  soil  upon  which 
shore  vegetation,  then  land  herbs  and  shrubs,  and  finally  trees 
grow. 

1116.  Structural  types  of  limnetic  plants.— There  are  certain 
types  of  plant  form  and  structure  in  relation  to  the  water  envi- 
ronment recognized.     These  are  as  follows: 

1.  The    quillwort    type.  —  Plants    submerged,    rooted    to    the 
soil,    with    rosette    habit    and    mostly    cylindrical    terete    leaves. 
This  type  is  represented  by  the  Isoetes,  or  quillwort  formation, 
the  Pilularia  formation,  water-lobelia  formation,  etc. 

2.  The  water-lily  type. —  Plants  floating  with  leaves  and  long 
flexile  petioles  or   stems   arising  from  creeping  or  subterranean 
perennial  rootstocks.   Examples :  white  water-lily  formation  (Cas- 
talia  odorata  =  Nymphaea   odorata),  yellow  water-lily    formation 
(Nymphaea     advena  =  Nuphar     ad  vena),    water- fern     formation 
(Marsilia    formation),    floating  pondweed   formation  (Potamoge- 
ton  natans  formation),  etc. 

3.  The  pondweed  type. — Plants  entirely  submerged,  rooting  to 
the  soil,  with  long  slender  floating  stems.     Examples:  most  of 
the  pondweeds  (Pondweed  formations),  Zannichellia  formation, 
Naias  formation,  Heteranthera  formation,  Myriophyllum  forma- 
tion, etc. 

4.  The  duckweed  type. — Free  floating  plants  with  short  stems, 
or  "fronds."     Examples:  duckweed  or  duckmeat  (Lemna)  for- 
mation, Riccia  formation  (Riccia  natans,  fluitans,  etc.),  Salvinia 
formation,  Azolla  formation,  etc. 

5.  The  river-weed,  or  fluvial,  type. — Plants  fastened  to  stones 
in   streams,   entirely  submerged,   stems  slender,   flexible,   frond- 
like,    leaves    not    differentiated.     Examples:    river-weed    (Podo- 
stemon)  formation,  Fontinalis  (fluvial  mosses)  formation.    Among 
the  algae  fluvial  forms  like  Cladophora,  Lemanea,  etc.,  belong  here. 

111.  Marine,  or  Pelagic,  Plant  Societies. 

1117.  By  far  the  larger  number  of  the  fixed,  or  benthonic, 
marine  plants  are  lithophytes  (attached  to  rocks),  and  the  larger 
number  of  these  are  algae.     The  larger  ones  are  attached  by 


628  RELATION    TO   ENVIRONMENT. 

disk-like,  or  lobed,  holdfasts,  while  the  diatoms  are  attached 
by  stems  of  gelatine.  A  large  number  of  the  smaller  ones  are 
epiphytes,  and  there  are  many  semiparasites  also  among  the 
algae,  as  well  as  some  fungus  parasites.  Very  few  marine  plants 
are  attached  to  the  mud  or  sandy  bottoms.  These  places  corre- 
spond to  deserts  in  the  paucity  of  their  flora.  The  few  plants 
found  here  (Caulerpa,  etc.)  are  attached  by  root-like  holdfasts, 
or  in  the  shallow  places  meadows  of  sea-grass  (Zostera)  are  found. 
The  larger  algae  are  almost  exclusively  confined  to  the  photic 
region  (extends  30/^-40^  =  100-125  feet  deep),  while  seed-plants 
are  exceptional. 

1118.  The  photic,  or  bright  light,  region  is  divided  into  two 
broad  zones;  the  upper  one  is  periodically  exposed  by  the  move- 
ment of  the  tide  and  lies  between  limits  of  ebb  and  flow.  The 
lower  zone  of  the  photic  region  lies  below  ebb-tide. 

1.  The  upper  photic  zone. — This  is  again  divided  into   two 
strata,  the  lower  one  being  the  most  favorable  for  development, 
since  the  members  are  only  partially  exposed  at  low  tide.     In 
the  upper  stratum  the  conditions  are  austere,  since  the  complete  and 
long  uncovering  exposes  the  plants  to  the  danger  of  drying  out. 
The  plants  are  generally  somewhat  stunted  in  growth,   stout, 
with  a  thick  epidermis,  and  are  sparingly  branched,  and  they 
are  exclusively  algae;   example,  Fucus  vesiculosus. 

2.  The  lower  photic  zone. — To  this  zone  belong  all  the  marine 
seed-plants  and  the  great  mass  of  algal  vegetation.      This  zone 
is  also  divided  into  strata,  dependent,  however,  upon  the  dimin- 
ishing intensity  of  light  at  increasing  depths.     It  is  interesting 
to  note  that  in  general  there  is  a  definite  relation  between  the  color 
of  the  algae  and  the  light  stratum  which  they   inhabit.      The 
green  algae  (Ulva,  Enteromorpha,  etc.)  are  chiefly  in  the  upper 
stratum,  the  brown  algae  (Laminaria,  etc.)  chiefly  in  the  middle 
one,  and  the  red  algae  chiefly  in  the  lower.     Yet  the  relation  be- 
tween the  color  of  the  algae  and  the  light  stratum  which  they 
inhabit  is  not  as  definite  as  was  once  supposed.     The  red  algae, 
however,  are  especially  adapted  to  growing  in  the  more  dimly 
lighted  stratum  of   the  photic  region,  since  they  are  sensitive 


AQUATIC   VEGETATION. 


629 


to  light  and  suffer  decoloration  in  the   stronger-lighted  strata. 
In  shady  places  the  red  algae  grow  nearer  the  surface;    some 


Fig.  S33&- 

Ascophyllum  nodosum  at  low  tide,  Hunter's  Island,  New  York  City.     (Photo- 
graph by  M.  A.  Howe.) 

species  are  bright  red  when  they  grow  in  the  shade  or  dull  red' 
when  growing  in  brighter  light. 


CHAPTER  LVH. 

PRACTICAL   STUDY   OF  PLANT    FORMATIONS. 

I.  Suggestions  for  Practical  Study  of  Plant 
Formations.* 

1119.  The  space  is  too  limited  in  this  work  to  present  an  elaborate  ot 
even  complete  plan  for  study  of  plant  formations.  The  purpose  is  to 
offer  merely  some  plain  suggestions  to  those  who  wish  to  make  a  general 
survey  of  plant  formations  in  a  given  region  where  time  is  limited  or  where 
it  is  desired  to  do  this  as  a  supplement  to  the  elementary  botanical  work 
of  the  school.  It  is  needless  to  say  that  the  student  should  have  had  a 
good  course  in  elementary  plant  physiology  and  general  morphology,  since 
these  subjects  are  fundamental  to  the  study  of  the  relation  of  vegetation 
to  its  environment. 

For  independent  study  of  plant  formations  more  than  an  elementary 
knowledge  of  these  subjects  is  necessary,  as  well  as  a  good  working  knowl- 
edge of  plant  classification.  This  the  elementary  student  cannot  possess, 
and  yet  it  is  possible  to  learn  many  useful  and  practical  things  concerning 
plant  life  which  will  not  only  aid  one  in  interpreting  the  relations  of  vege- 
tation to  natural  surroundings,  but  will  give  a  broader  view  of  nature. 

The  work  should  be  done  under  the  guidance  of  the  teacher.  Even  if 
the  students  know  but  few  plants,  it  will  be  possible  for  them  to  discover 
striking  formations  where  the  individuals  of  one  or  several  species  are 
massed  together  over  a  considerable  area  so  that  they  form  the  dominant 
vegetation  of  the  area.  They  can  be  told  the  name  of  the  plant  unless 
it  is  possible  for  them  to  discover  it  for  themselves,  and  it  should  be  borne 
in  mind  that  it  is  more  important  to  discover  a  life  relation  of  the  plant 
in  this  way  than  it  is  to  merely  determine  the  name  of  the  plant.  Then 
the  prominent  plant  formations  can  be  worked  out  for  several  different 


*  See  Suggestions  for  Teacher,  foot-note  page  349,  Chapter  XXXVIII. 

630 


PRACTICAL    STUDY  OF  PLANT   FORMATIONS.      63! 

physiographic  areas.  It  should  be  borne  in  mind  always  that  all  asso- 
ciations of  plants  do  not  represent  distinct  formations.  Some  formations 
may  be  incipient  and  others  decadent  and  thus  difficult  to  determine;  also 
more  or  less  extensive  areas  may  have  a  mixture  of  several  formations 
over  a  transition  area.  Again,  mere  patches  representing  a  gregarious 
condition  of  certain  species  within  another  formation  should  not  be  mis- 
taken for  a  formation. 

The  district  selected  for  study  should,  if  possible,  include  forest,  low 
marshy  areas,  and  ponds  or  lakes,  within  which  area  will  probably  occur 
a  number  of  different  soil  conditions,  as  rocky,  sandy,  or  clayey  areas, 
etc.,  ravines,  bluffs,  meadows,  etc.  It  might  be  well  to  follow  the  plan  of 
mapping  the  area,  or  of  mappi  g  the  distinct  physiographic  areas  studied 
when  they  are  far  separated,  and  indicating  the  location  and  extent  of 
different  formations,  with  notes  on  kind  of  soil  (gravel,  sandy,  rocky, 
loamy,  etc.),  and  in  general  the  relation  of  the  formations  to  topography, 
i.e.,  to  different  degrees  of  the  gradient  of  slope  where  there  is  radial 
or  lateral  topographic  symmetry,  as  on  hillsides  or  borders  of  streams,  or 
ponds,  etc.,  different  depths  of  water,  etc.  Topographic  maps  already  in 
existence  can  be  used  or  made  the  basis  of  the  special  chart.  The 
topographic  maps  now  being  issued  by  the  United  States  Geological 
Survey  *  are  most  excellent  for  use  and  reference  in  connection  with  this 
study. 

The  district  studied  would,  of  course,  be  more  or  less  limited.  In  con- 
nection with  the  work  studies  of  literature,  or  lectures  should  connect  the 
work  with  larger  districts  and  with  the  great  climatic  formations,  or  vege- 
taiton  provinces,  or  regions  (See  Section  II  of  this  chapter). 

Suppose  the  district  to  be  studied  lies  within  the  woodland  climate. 
For  practical  purposes  of  an  elementary  study  this  could  be  divided  into 
mountain  districts,  and  coastal  plain,  and  continental  valley  districts,  since 
in  a  mountain  region  one  would  be  chiefly  concerned  with  problems  some- 
what different  from  those  of  the  coastal  plains  or  continental  valleys,  and 
the  two  sets  of  districts  could  only  be  studied  together  in  actual  practice 
when  the  work  was  extended  over  a  long  period.  For  the  purpose  of 
subdividing  a  large  area  and  getting  at  the  chief  physiographic  areas  which 
are  the  units  of  the  principal  formations  the  more  level  districts  of  the 
woodland  climatic  region  might  be  divided  as  follows: 


*  From  the  U.  S.  Geological  Survey  at  Washington,  D.  C.,  can  be  ob- 
tained a  map  showing  on  a  small  scale  the  districts  covered  for  each  State 
and  indicating  which  ones  are  completed,  as  well  as  the  price.  By  secur. 
ing  this  map  one  can  easily  determine  the  topographic  maps  needed  to 
cover  the  area  selected  for  study. 


632 


RELATION    TO  ENVIRONMENT. 


1120.  Woodland  climatic  region. 


Forested  Areas. 


Non-forested  Areas. 


Series  of               Principal 
Formations.         Formations. 

Series  of               Principal 
Formations.          Formations. 

f  Rock  hill. 

(  Mud       or       reed 

'  i.  Upland     1   Gravel  hill. 

swamp. 

series.  1   Sand  hill. 

Sphagnum  moor. 

L  Clay  hill. 

Heath  moor. 

Rock  areas. 

Tamarack  swamp. 
Meadows. 

u 
.S3 

2.  Lowland 
series. 

Gravel  areas. 
Sand  areas. 
Clay  areas. 

i.  Edaphic 
series. 

Rocky  places. 
Sandy  strand  and 
dunes. 

^ 

[  Loam  areas. 

Salt  marsh. 

<U     en 
^     C 
oj     o 

Ravine. 

Alkali  lands. 

«—  i   *!> 

River  bluff. 

Shores     of      marl 

rt  .5 
1   ° 

3.  River.        , 

Flood  plain. 

[      ponds. 

series. 

Mature  river  val- 

• Streams. 

C    A 

o   g 

ley. 

Ponds. 

if 

'  Mangrove  swamp. 
Heath  moor. 

2.  Aquatic 
series. 

Lakes. 
Salt  seas. 

.s  ^ 
s 

4.  Swamp 
series. 

Mud  swamp. 
Water  swamp. 

Ocean. 

Brackish  waters. 

•i 

Tamarack  swamp. 

.  Marl  ponds. 

to 

i 

.  Cypress  swamp. 

3.  Culture     (  Cultivated  places. 

u 

f  Lake  bluff. 

series.  \  Waste  places. 

Ocean  bluff. 

5.  Coastal     J  Sand     strand     or 
series.            dunes. 

(No  attempt  is  made  here 
to  subdivide  the  culture 

1  Humus  strand. 

series.) 

Coastal  swamp. 

New  features  and  combinations  will  present  themselves  in  each  district 
studied.  The  above  outline  must  be  modified  to  suit  the  particular  case. 
In  some  cases  formations  in  the  district  may  not  be  represented.  Special 
.formations  may  occur  not  explicitly  referred  to  in  the  synopsis.  The 
discovery  and  elaboration  of  these  regions  would  be  especially  interesting. 

1121.  In  the  mountain  districts,  besides  the  physiographic  divisions 
the  climatic  divisions  would  be  noticeable  within  short  distances  as  com- 
pared with  the  more  level  districts.  A  general  subdivision  might  be 
made  as  follows: 


PRACTICAL  STUDY  OF  PLANT  FORMATIONS.      633 

Montane  Districts. 

1.  Valley  series. 

2.  Foothill  series. 

3.  Basal  series. 

4.  Montane  series. 

5.  (Alpine  series  beyond  tree  growth). 

In  general  physiographic  divisions  might  be  made  similar  to  those  given 
in  the  table  above  for  the  more  level  districts,  though  modifications  and 
additions  would  be  necessary  when  an  actual  survey  of  the  district  is  made. 
So  in  the  following  climatic  regions  a  similar  physiographic  division  might 
be  made,  but  some  alterations  and  additions  would  be  necessary  because 
of  changed  conditions  of  environment.  For  example,  the  oases  in  deserts 
and  plains,  the  warm  oases,  and  the  tundra  in  arctic  regions,  and  so  ,on. 

Prairie   climatic  region.  )  _, 

Plains   climatic  region.   [  Grassland  climatic  region  of  Schimper. 

Arctic   climatic   region. 

While  the  physiographic  subdivisions  of  districts  outlined  above  is  only 
suggested  as  a  basis  for  an  elementary  practical  study  of  vegetation  of 
local  regions,  the  locality  should  be  asssigned  its  proper  place  in  some 
one  of  the  several  plans  proposed  for  the  purpose  of  dividing  the  vegeta- 
tion surface  of  the  earth  into  large  natural  areas  based  either  on  physio- 
graphic or  climatic  conditions  or  both.  See  Section  II  of  this  chapter. 

1122.  Formations  (=  association  of  some  students'). — Having  looked  over 
the  locality  or  district  to  be  studied,  and  having  prepared  a  chart  showing 
the  distinct  physiographic  areas  or  edaphic  areas  to  be  examined  in  detail, 
these  principal  formations  can  then  be  critically  studied  for  the  purpose 
of  determining   the    individual   formation,   or  formations   (=  associations 
of  some  students). 

1123.  Dominant   species  in  a  formation. — (i)    Determine   the   different 
formations  with  the  one  or  more  dominant  species. 

(2)  Chart  its  extent  and  limits  in  the  locality  or  principal  formation. 

(3)  If  there  are  evident  layers  (as  in  a  forest  or  heath),  determine  the 
prominent  ones. 

(4)  Where  there  is  a  slope  providing  a  regular  succession  of  series  of 
different  soil  conditions  or  water  content,  or  a  sloping  shore  and  water 
basin,   determine  the  zones  (or  lateral  layers)   indicated   by  the  different 
individual    formations  down  the  sloping  bank  and  gradually  out  into  the 
deep  water.     Even  where  topographic  conditions  are  the  same  the  ground 
may  be  occupied  by  different  species  in  different  regions  or  at  different 
points  along  the  same  shore.     All  these  peculiarities  should  be  noted  and 
the   formations  of  different  lakes,    ponds,   etc.,   compared.     For  example, 
in  fig.  534  are  shown  several  zonal  formations.     Beginning  at  the   highest 


634 


RELATION    TO  ENVIRONMENT. 


PRACTICAL   STUDY  OF  PLANT  FORMATIONS.      635 


point  on  the  land  these  are  in  succession:  white  pine  (i),  oak  (2),  willows 
(3),  thoroughwort  (4):  littoral  zone  of  semi-aquatics,  typha  (5),  bulrushes 
(6),  arrow-leaf  (7);  mid  zone,  pond-lilies  and  potamogetons  (8);  Sub- 


Land  Zone. 


Littoral  Zone. 


Mid  Zone. 


Submerged  Zone. 


*         € 
«          & 


ait 


Willow  Formation 
(Salicetum). 


Eupatorium 

Formation 

(Eupatorietum). 


Typha  Formation 
(Typhetum). 


Bulrush  Formation 
(Scirpetum). 


Arrow-leaf  Formation 
(Sagittarietum). 


Pond-lily  Formation 
(Nymphetum). 


}.    Pondweed  Formation 
i     (Potamogetonetum). 


Bassweed  (Chara) 

Formation 
(Charetum) 


Fig.  535. 
Chart  showing  relative  position  of  plant  formations  in  zones  along  lake  shores. 

merged  zone,  pondweeds  (Potamogeton  and  Vallisneria,  9),  bassweed 
(Chara,  10).  By  the  side  of  this,  on  the  same  shore,  the  typha  is  replaced 
by  sedges,  and  the  arrow-leaf  by  the  yellow  water  lily  or  spatter-dock  (Nu- 


OO    OOOft  Oa 
DO    OO     OOOOOO 

to   o°o  oo  oooo 
oo    0  0  0.0   oooo<f 

O    OoO    0    OOOO<> 


636  RELATION   TO  ENVIRONMENT. 

phar  ad  vena),  while  in  some  other  places  the  latter  is  replaced  by  the  white 
water-lily  (Nymphaea  odorata).     These  could  be  charted  as  in  fig.  535. 

(5)  Note  the  prominent  physical  characteristics  of  the  soil. 

(6)  Note  exposure  to  sun,  wind,  etc.,  if  so  situated  as  to  be  especially 
influenced  by  these. 

1124.  Secondary  or  subordinate  species   in   a  formation. — Give  special 
attention  to  those  species  which  are  characteristic  of  similar  physiographic 
areas. 

(1)  Species  which  occupy  similar  ground  in  other  districts  where  they 
may  become  dominant  species  in  the  formation  (example,  cranberries  occur  as 
scattered  individuals  in  some  moors  or  bogs,  while  in  others  they  are  domi- 
nant species  in  the  formation,  so  it  is  with  the  cattail-flag  in  swamps,  and 
with  many  other  plants). 

(2)  Species  which  are  characteristic  of  certain  localities  but  are  never 
abundant  enough  to  dominate  the  formation  (examples:  the  pitcher  plant, 
sundews,  etc.,  in  moors). 

(3)  Species  which  are  infiltrated  in  with  the  dominant  vegetation  of  a 
formation  and  mark  this  portion  off  from  other  patches  of  the  same  forma- 
tion (example,  in  rolling  prairies  or  grass-land,  different  flowers  on  different 
kinds  of  soil  or  where  there  is  a  slight  variation  in  soil  moisture). 

(4)  Guilds  (or  associates  or  companions)  (examples:  Lianas  [scramblers, 
climbers,  root-climbers],  etc.),  epiphytes  (examples:  Lichens,  mosses,  etc.). 

(5)  Parasites  (examples:  parasitic  fungi  on  leaves,  fruit,  flowers,  trunks, 
etc.,  parasitic  flowering  plants,  as  dodder,  etc.). 

(6)  Wood-destroying  fungi. 

(7)  Humus-forming  fungi,  and  so  on. 

1125.  The  general  features  of  the  study  the  teacher  can  illustrate. — ist. 
By  lantern  slides  of  photographs  of  vegetation  and  formations  of  different 
regions  not  illustrated  in   the   local  flora  (examples:  desert,  arctic,  alpine, 
prairie,  plains,  forests  of  different   kinds,  edaphic  series  of  various  kinds). 

2d.  By  photographs  illustrating  different  physiographic  areas,  or 
edaphic  series,  or  principal  formations,  to  be  studied  in  the  selected  locality. 
These  will  also  show  many  individual  formations  in  zones  or  areas.  The 
negatives  could  be  used  to  make  velox  prints  or  blue  prints  for  members 
of  the  class  to  illustrate  their  study,  each  student  purchasing  a  set. 

3d.  It  is  desirable,  so  far  as  possible,  to  have  at  least  a  small  collection 
of  plants  especially  made  to  illustrate  various  features  of  the  study  (examples: 
plants  from  arctic,  alpine,  desert,  and  other  regions,  especially  such  as 
will  illustrate  such  characters  as  fit  them  to  exist  under  the  peculiar  con- 
ditions, as  well  as  to  illustrate  plants  which  are  dominant  elements  of  char- 
acteristic formations).  In  some  cases  these  can  be  obtained  by  purchase 
or  exchange.  In  addition  the  teacher  can  work  each  year  toward  making 
a  collection  of  local  plants  fo-  the  purpose  of  illustrating  the  various  phases 


PRACTICAL   STUDY  OF  PLANT  FORMATIONS.      637 

of  the  subject.  In  this  work  the  teacher  can  probably  enlist  the  cooperation 
of  some  of  the  students.  In  many  cases  photographs  will  illustrate  cer- 
tain features  of  the  plant  not  well  shown  in  a  dried  specimen,  and  the  photo- 
graph can  accompany  it.  Access  to  greenhouses  will  enable  the  teacher 
to  further  illustrate  the  subject. 

1126.  The  student  should  so  far  as  possible  keep  a  neat  record,  brief, 
but  to  the  point,  of  his  work.  This  record  should  be  supplemented  by 
preserved  plants,  or  good  photographs  of  the  plants  (or  both),  the  notes 
indicating  the  principal  and  individual  formations  to  which  it  belongs, 
whether  a  dominant  species  in  a  formation,  whether  alone  or  coordinate 
with  other  species  (preserve  and  cite  them),  or  if  a  subordinate  species 
then  note  what  relation  it  bears  to  the  formation  or  the  locality;  also  a 


Ridges  with  Pinus  divaricata. 
Zone  of  Larix  laricina. 
Zone  of  Picea  Mariana. 


a  Zone  of  Ledum  and  Eriophorum. 

!      \ 1     Central  Sphagnum  and  Ulricularia. 

Fig.  536. 
McMillan,  Bull.  Torr.  Bot.  Club,  p.  502,  1896. 

few  notes  to  indicate  kind  of  soil  (or  depth,  etc.,  of  water  in  case  of  aquat- 
ics); and  a  reference  to  a  photograph  where  possible  to  show  character 
of  formation  and  surroundings.  With  a  numbered  series  of  photographs, 
one  print  would  do  duty  in  some  cases  for  citation  of  several  or  a  large 
number  of  species.  Cards  or  blank  paper  5X8  inches  might  be  used  by 
the  students  to  keep  their  record,  one  card  or  slip  for  each  species,  the 


638  RELATION   TO  ENVIRONMENT. 

name  being  written  in  the  upper  left-hand  corner,  and  these  cards  could 
then  be  kept  in  card-catalogue  order.  When  necessary  notes  and  references 
could  be  continued  on  back. 

1127.  Simple  way  to  chart  extent  and  relation  of  plant  formations. — 
There  are  several  simple  ways  of  charting  the  location  and  extent  of  plant 
formations.     One  method  of  illustrating  the  relation  of  formations  to  each 
other  is  shown  in  fig.  535.     The  relation  and  extent  of  formations  may  be 
illustrated  as  shown  in  fig.  536  (from  MacMillan,  Bull.  Torr.  Bot.  Club, 
23,  p.  502,  1896),  and  as  shown  by  Pieters  (The  Plants  of  Lake  St.  Clair, 
Bull.  Mich.  Fish  Comm.,  No.  2,  1894,  Lansing),  by  Ganong  (Vegetation  of 
Bay  of  Fundy  Marshes,  Bot.  Gaz.,  36,  p.  351,  1903),  and  others. 

II.  Natural  Vegetation  Regions  of  the  Earth. 

1128.  According  to    Griesebach. — The   regions   established    by   Griese- 
bach  were  based  on  the  notion  of  separate  centers  of  development  and 
distribution  of  the  vegetation  of  the  land. 

Twenty-four  regions  were  recognized: 

I.  Arctic  region.  XIII.  Prairie  region. 

II.  Forest  region  of  the  Eastern  XIV.  Calif ornian  Coast  region. 

Continent.  XV.  Mexican  region. 

III.  Mediterranean  region.  XVI.  West  Indies  region. 

IV.  Region  of  the  Asiatic  Steppes.  XVII.  Cisequatorial  South  Ameri- 
V.  Chinese-Japanese  region.  can  region. 

VI.  Indian-Malayan  region.  XVIII.  Hylaea,      or       Amazonian, 

VII.  Sahara  region.  region. 

VIII.  Soudan,    or    Central    Africa,  XIX.  Brazilian  region. 

region.  XX.  Tropical  Andes  region. 

IX.  Kalahari  region.  XXI.  Pampas  region. 

X.  Cape  of  Good  Hope  region.  XXII.  Chilean  transition  region. 

XI.  Australian  region.  XXIII.  Antarctic  forest  region. 

XII.  Forest  region  of  the  Western  XXIV.  Oceanic  Island  region. 

Continent. 

1129.  According  to  Engler. — Engler's  classification  is  based  on  the  notion 
of  general  development  and  migration.     He  recognizes  four  great  realms, 
which  are  then  divided  into  a  large  number  of  regions  and  provinces.     Only 
those  regions  and  provinces  will  be  given  here  which  apply  to  North  America, 

I.    THE    REALMS    AND   THE    REGIONS    IN   NORTH    AMERICA. 
World-realms.  Region  in  North  America. 

(1)  .\rctic  region  (also  in  Europe). 

(2)  Subarctic  or  Conifer  region  (also 


A.  Northern  extratropical  Realm.. 


in  Europe). 

(8)  Pacific  N.  A.  region. 

(9)  Atlantic  N.  A.  region. 


PRACTICAL   STUDY  OF  PLANT  FORMATIONS.      639 

World-realms.  Region  in  North  America. 
B.  Tropical  old-world  Realm. 

(1)  Mexican  highland  region. 

(2)  Tropical  American  region. 

(These  parts  of  North  America 


C.  South  American  Realm. . 


are    considered    as    belonging    to 
the  Southern  Realm.) 
D.  Old  Oceanic  Realm. 

2.    PROVINCES    IN    NORTH    AMERICA. 

(1)  Arctic  Region,  not  subdivided. 

(2)  Subarctic,  or  Conifer  Region  (only  those  in  North  America  given). 

(c]  North  American  Lake  Province  (unites  on  the  north  with  the 
arctic  region  and  on  the  south  with  the  Pacific  and  Atlantic  regions 
of  North  America). 

The  regions  of  the  North  American  continent  come  under  two  realms, 
as  is  noted  above.  Mexican  highlands  and  Central  America  botanically 
belong  rather  with  South  than  with  North  America.  (Three  zones  are 
recognized:  I,  the  Algonquin  zone,  lying  between  Hudson  Bay,  Newfound- 
land and  Lake  Superior,  characterized  by  Thuja  occidentalis  and  Taxus 
canadensis;  II,  Athabasca  zone,  bounded  on  the  south  by  a  line  from 
Hudson  Bay  to  the  Rocky  Mountains  and  characterized  by  Pinus  banksiana, 
Abies  balsamea,  Picea  nigra,  Larix  pendula,  Picea  alba;  III,  Canadian 
zone,  not  clearly  delimited,  lying  southward  of  the  other  two  and  between 
them,  including  Manitoba,  western  Ontario,  northern  Minnesota,  Wiscon- 
sin and  Michigan,  characterized  by  Pinus  strobus,  Pinus  resinosa,  and 
Abies  canadensis.) 

(3)  Pacific  North  American  Region.     (Reaching  from  the  sea  to  the 
foot  of  the  Rocky  Mountains,  and  south  to  the  Mexican  highlands.) 

(a)  Californian  coast  province  (between  the  Coast  Range,  and  the 
sea.  Characteristic  conifers,  Sequoia  sempervirens,  Pinus  insignis, 
Pinus  muricata,  Pinus  tuberculata,  Pinus  coulteri,  Picea  bracteata, 
Torreya  calif ornica,  Cupressus  macnabiana,  Cupressus  macrocarpa). 

(6)  Oregon  province.  (Including  area  west  of  Cascade  Mountains.) 
Four  zones  are  recognized:  I,  Kaloschen  zone,  to  52°  north  latitude, 
characterized  by  Thujopsis  borealis;  II,  Douglas  zone,  to  43°  north 
latitude,  characterized  by  Abies  douglasii;  III,  Umpqua  zone,  between 
42°  or  43°  north  latitude,  characterized  by  Cupressus  fragrans;  IV, 
Sierra  zone,  characterized  by  Pinus  lambertiana  and  Sequoia  gigantea 
(=S.  washingtoniana). 

(c)  Rocky  Mountain    province.      (Characterized   by  Pinus   flexilis, 
Pinus  monophylla,  Larix  occidentalis,  etc.) 

(d)  Colorado  province.     (Reaching  from  Cascade  to  Rocky  Moun- 
tains, open  country). 


640  RELATION  TO  ENVIRONMENT. 

(4)  Atlantic  North  American   Region. 

(a)  Appalachian  province.  (The  forest  district  of  the  Atlantic 
North  American  region  south  of  the  lake  province  includes  three 
zones:  I,  Alleghany  zone,  characterized  by  Pinus  inops,  Pinus  pun- 
gens,  Pinus  rigida,  Picea  fraseri,  Juniperus  virginiana;  II,  Carolina 
zone,  including  New  Jersey,  Delaware,  Maryland,  Pennsylvania,  Vir- 
ginia, Georgia;  III,  Mississippi  zone,  including  the  forest  district  of 
the  Mississippi  valley.) 

(£)  Prairie  province.  (The  western  central  and  central  prairies  of  the 
Atlantic  drainage,  including  also  the  Saskatchewan  and  Assiniboian 
prairies  of  Arctic  Ocean  drainage.) 

1130.  According  to  Drude. — This  is  one  of  the  most  recent  and  general- 
ized divisions  of  the  earth  into  botanical  realms  and  regions,  and  is  used  by 
MacMillan,  Pound  and  Clements,  and  others. 

THE  FLORAL  REGIONS   OF   CONTINENTS   AND   ISLANDS. 

Realms.  Regions. 

(1)  Arctic  region. 

(2)  Northern  region. 

(3)  Middle  Norh  American  region. 

(4)  Mediterranean-Oriental  region. 

(5)  Lower  Asian  region. 
L  (6)  East  Asian  region. 


A.  Northern  Realm 


B.  Tropical  Realm. 


(1)  Tropical  American  region. 

(2)  Tropical  African  region. 

(3)  Indian  region. 

(4)  Malayan-New  Zealand  region. 

(1)  Andes  region. 

(2)  South  African  region. 
C.  Southern  Realm ^   (^  Australian  re?ion> 

(4)  Antarctic  region. 

THE   FLORAL   REGIONS    OF   THE   OCEAN. 

Only  one  realm  in  the  ocean  is  recognized. 
The  regions  are  as  follows: 

A.  Northern.  B.  Tropical. 

1.  Arctic  coasts.  4.  Mediterranean  coasts. 

2.  North  Atlantic  coasts.  5.  Tropical  Atlantic  coasts. 

3.  North  Pacific  coasts.  6.  Indian  coasts. 

7.  Tropical-Pacific  coasts. 

C.  Southern. 

8.  Australian  coasts. 

9.  Antarctic  coasts. 


P RADICAL   STUDY  OF  PLANT  FORMATIONS.     641 

1131.  According  to  Merriam. — The  most  recent  arrangement  of  vegeta- 
tion regions  as  applied  to  North  America  are  the  life  zones  and  areas  of 
Merriam,  which  are  based  on  the  climatic  factors,  temperature  and  moisture, 
the  influence  of  temperature  being  most  important  during  the  period  of 
growth  and  reproduction.  These  life  zones  and  areas  have  been  worked 
out  more  largely  with  reference  to  animals,  though  plants  have  been  con- 
sidered also,  and  Merriam  believes  that  the  distribution  of  plants  as  well  as 
animals  is  limited  by  these  life  zones.  For  a  discussion  of  them  see  Chap- 
ter XL VIII ;  see  also  fig.  492. 

LIFE  ZONES  AND  AREAS   OF   NORTH   AMERICA. 
Zones.  Areas. 


f  Arctic,  or 
•  Arctic-alpine. 

Boreal Hudsonian. 

[  Canadian. 

l  Alleghanian. 

Transition •<  Arid  transition. 

'  Pacific  coast  transition. 

.   Upper  Austral (Carolinian. 

Austral 1  (  Upper  Sonoran. 

Lower  Austral j  Austroriparian. 

( Lower  Sonoran. 
Semitropical  Gulf  strip. 

j  Humid  tropical. 

(  Arid  tropical. 

2.   CHARACTERISTICS   OF   THE  ZONES   AND   AREAS. 

1132.  Briefly  the  limits  and  characteristic  plants  of  the  zones  and  areas 
are  as  follows: 

BOREAL  REGION. — There  are  three  natural  belts. 

1.  Arctic  or  Arctic-Alpine  Zone. — This  is  the  northernmost  belt  and  lies 
beyond  the  limit  of  tree  growth.     The  larger  part  is  perpetually  covered 
with  snow  and  ice.     It  is  characterized  by  extensive  fields  of  mosses,  by 
the  arctic  poppy,  dwarf  willows  and  various  saxifrages,  as  well  as  other 
arctic    plants,    and    by    some    writers   is    called    the    hyperboreal    region. 
Within  the  United  States  the  Arctic-Alpine  zone  is  restricted  to  the  area 
above  timber  line  on  the  summits  of  high  mountains.     It  is  inhabited  by 
arctic-alpine  plants  and  animals,  and  is  far  too  cold  for  agriculture. 

2.  The  Hudsonian  Zone. — This  is  a  subarctic  zone  embracing  the  most 
northern  part  of  the  great  transcontinental  coniferous  forests — a  forest 
of  spruces,  firs,  birches,  and  aspens,  stretching  from  Labrador  to  Alaska 
in  the  region  of  Hudson's  Bay.     By  its  position  it  is  sometimes  called 


642  RELATION    TO   ENVIRONMENT. 

the  Northern  Foerst,  or  because  of  the  large  number  of  lakes  in  the  zone, 
the  Lacustrian  Forest  of  the  North.  It  includes  also  the  upper  timbered 
slopes  of  the  higher  mountains  of  the  United  States  and  Mexico.  In  the 
eastern  United  States  the  Hudsonian  zone  is  restricted  to  the  cold  sum- 
mits of  the  highest  mountains,  where  it  occurs  in  the  form  of  a  chain  of 
widely  separated  islands  reaching  from  northern  New  England  to  western 
North  Carolina.  Like  the  preceding,  this  zone  is  of  no  agricultural  im- 
portance. 

3.  The  Canadian  Zone. — The  Canadian  zone  comprises  the  southern 
part  of  the  great  transcontinental  coniferous  forest  of  Canada,  the  northern 
parts  of  Maine,  New  Hampshire,  and  Michigan,  a  strip  along  the  Pacific 
coast  reaching  as  far  south  at  least  as  Cape  Mendocino  in  California,  and 
the  greater  part  of  the  high  mountains  of  the  United  States  and  Mexico. 
In  the  east  it  covers  the  Green  Mountains,  Adirondacks,  and  Catskills, 
and  the  higher  mountains  of  Pennsylvania,  West  Virginia,  Virginia,  western 
North  Carolina,  and  eastern  Tennessee.  In  the  mountains  of  the  east  it 
covers  the  lower  slopes  in  the  north  and  the  higher  slopes  in  the  south. 
In  the  Rocky  Mountain  region  it  appears  to  reach  continuously  from 
British  Columbia  to  west  central  Wyoming;  and  in  the  Cascade  Range, 
from  British  Columbia  to  southern  Oregon,  with  a  narrow  interruption 
along  the  Columbia  River.  Pines,  spruces,  firs,  hemlock  spruce, 
larches,  etc.,  outnumber  the  broad-leaved  deciduous  trees.  Counting  from 
the  north,  this  zone  is  the  first  of  any  agricultural  importance.  Wild 
berries— as  currants,  huckleberries,  blackberries,  and  cranberries — grow 
in  profusion,  and  the  beechnut  (in  the  east)  is  an  important  food 
of  the  native  birds  and  mammals.  In  favored  spots,  particularly 
along  the  southern  border,  white  potatoes,  turnips,  beets,  and  the  more 
hardy  Russian  apples  and  cereals  may  be  cultivated  with  more  moderate 
success. 

THE  AUSTRAL  REGION. — This  includes  three  zones  and  seven  areas. 

Transition  Zone. — As  its  name  indicates,  this  zone  is  the  ground  where 
the  boreal  and  austral  types  meet.  The  forests  are  chiefly  of  deciduous 
trees  which  grow  in  the  cooler  austral  belt. 

a.  Alleghanian  Area. — This  is  the  humid  eastern  division.  It  ex- 
tends from  the  coast  of  New  England  across  New  York,  Pennsylvania, 
southern  Ontario,  Michigan,  Wisconsin,  Minnesota,  and  the  Dakotas, 
when  it  meets  the  dry,  grassy  plains  of  the  west.  In  the  east  it  reaches 
southward  in  a  long  arm  including  the  Alleghany  Mountains  to  Georgia. 
Oaks,  hickories,  chestnuts,  locusts,  birches,  aspens,  ash,  and  mountain 
ash  mingle  with  the  northern  spruces,  hemlock  spruce,  pines,  and  other 
coniferous  trees  from  the  south,  while  the  shrubby  undergrowth  is  charac- 
terized by  azaleas,  rhododendrons,  andromedas,  and  other  heaths.  Oats, 
rye,  wheat,  Indian  corn,  the  potato,  onion,  root  crops  like  the  beet,  carrot, 


PRACTICAL   STUDY  OF  PLANT  FORMATIONS.      643 

turnip,    etc.,    are   cultivated,    while   orchard   crops    like   apples,    peaches, 
cherries,  pears,  plums,  and  a  variety  of  berries  are  common. 

b.  The  Arid  Transition  Area. — "The  western  or  arid  division  of  the  Tran- 
sition zone  comprises  the  western  part  of  the  Dakotas,  northern  Montana 
east  of  the  Rocky  Mountains,  southern  Assiniboia,  small  areas  in  Mani- 
toba and  Alberta,  the  higher  parts  of  the  Great  Basin  and  the  plateau 
region  generally  (except  the  boreal  mountain  areas),  the  eastern  base  of 
the  Cascade-Sierra  system,  and   local  areas  still  farther  west,  in  Oregon 
and  California,  where  it  merges  into  the  humid  Pacific  Coast  division." 
The  prevailing  type  of  vegetation  is  the  true  sage-brush  (Artemisia  tri- 
denta)   with  extensive  tracts  of  the  yellow  or  bull  pine.      Wheat,   oats, 
barley,  corn,  apples,  cherries,  grapes,  pears,  plums,   potatoes,  sugar-beets, 
etc.,  are  cultivated. 

c.  The  Pacific  Coast  Transition  Area. — "The  humid  Pacific  Coast  divi- 
sion of  the  Transition  zone  comprises  the  western   parts  of  Washington 
and  Oregon  between  the  coast  mountains  and  the  Cascade  Range,  parts 
of  northern  California  from  near  Cape  Mendocino  southward  to  the  Santa 
Barbara  Mountains.     To  the  south  and  east  it  passes  into  the  Arid  Tran- 
sition, and  in  places  into  the  Upper  Sonoran."     This  region,  as  a  whole,  is 
one  of  great  humidity.     "The  northern  and  more  humid  part  is  covered 
by  a  magnificent  coniferous  forest,   carpeted   with   moss  and   ferns,   and 
often  choked   with  undergrowth.     The   prevailing  trees   are   Douglas   fir, 
Pacific  cedar,  western  hemlock,  and  Sitka  spruce,  whose  majestic  trunks 
attain  an  average  height  of  more  than  200  feet.     There  are  also  many 
broad-leaf    maples,   tree-alders,   madronas    and    western    dogwoods,    and 
numerous  kinds  of  shrubs,"  as  sabal  (Gaultheria  shallon),  thimble-berry 
(Rubus    nootkanus),    Oregon  grape   (Berberis   nervosa),   and  devil's-club 
(Echinopanax  horridula). 

"The  region  as  a  whole  is  one  of  relatively  uniform  temperature,  the 
wide  seasonal  differences  usual  in  other  parts  of  the  Transition  zone  being 
unknown.  The  temperature  of  the  summer  season,  the  hottest  part  of  the 
year,  is  phenomenally  low  for  the  latitude,  enabling  northern  or  boreal 
types  to  push  south  as  far  as  latitude  35°.  On  the  other  hand,  the  summer 
season  is  so  prolonged  (from  the  standpoint  of  temperature)  that  the  total 
quantity  of  heat  for  the  entire  season  is  phenomenally  high  for  the  latitude, 
enabling  southern  or  austral  species  to  push  north  as  far  as  Puget  Sound, 
where  the  total  quantity  of  heat  is  even  greater  than  at  Philadelphia,  Pitts- 
burg,  Cleveland,  and  Omaha,  although  Puget  Sound  is  500  miles  north 
of  the  latitude  of  these  places.  Even  at  Cape  Flattery — the  extreme  north- 
western point  of  the  United  States — which  is  exposed  throughout  the  year 
to  the  cold  coast  fogs,  the  total  quantity  of  heat  is  500°  F.  greater  than 
at  Eastport,  Maine,  although  the  latter  is  the  more  southern  locality  and 
has  the  higher  mean  summer  temperature.  The  low  summer  temperature 


644  RELATION    TO  ENVIRONMENT. 

along  the  Pacific  coast  permits  northern  species  to  come  far  south,  while 
the  high  sum  total  enables  southern  species  to  push  northward  as  far 
as  Puget  Sound.  Such  an  extensive  overlapping  of  Boreal  and  Austral 
faunas  does  not  occur  elsewhere  in  North  Amerca,  and  for  the  evident  reason 
that  no  area  approaching  it  in  extent  has  so  equable  a  temperature. 

"In  most  parts  of  the  United  States  it  is  easy  to  distinguish  the  bound- 
aries between  the  Transition  and  Upper  Austral  zones,  but  in  the  Pacific 
Transition  area  these  distinctions  are  nearly  obliterated,  a  large  portion 
of  the  species  ranging  in  common  over  both  belts." 

The  Upper  Austral  Zone. — "The  Upper  Austral  zone  may  be  divided 
into  two  large  and  important  faunal  areas — an  eastern  humid  or  Carolinian 
area  and  a  western  arid  or  Upper  Sonoran  area,  which  pass  insensibly 
into  one  another  in  the  neighborhood  of  the  one-hundredth  meridian." 

a.  The   Carolinian   Area. — "The   Carolinian   area  occupies   the   larger 
part  of  the  Middle  States,  except  the  mountains,  covering  southeastern 
South  Dakota,  eastern  Nebraska,  Kansas,  and  part  of  Oklahoma;  nearly 
the  whole  of  Iowa,  Missouri,  Illinois,  Indiana,  Ohio,  Maryland,  and  Dela- 
ware;   more  than  half  of  West  Virginia,  Kentucky,  Tennessee,  and  New 
Jersey,   and  large  areas  in  Alabama,   Georgia,   the   Carolinas,   Virginia, 
Pennsylvania,    New    York,    Michigan,    and    southern    Ontario.     On    the 
Atlantic  coast  it  reaches  from  near  the  mouth  of  Chesapeake  Bay  to  south- 
ern Connecticut,  and  sends  narrow  arms  up  the  valleys  of  the  Connecticut 
and  Hudson  rivers.      A  little  farther  west  another  slender  arm  is  sent 
northward,  following  the  east  shore  of  Lake  Michigan  nearly  or  quite  to 
Grand  Traverse  Bay.     These  arms,  like  nearly  all  narrow  northern  pro- 
longations of    southern  zones,  do  not  carry  the  complete  faunas  of  the 
areas    to    which    they  belong,   but    lack  certain  species  from    the  start 
and  become  more  and  more  dilute  to  the  northward  until  it  is  hard  to  say 
where  they  really  end.     Their  northward  boundaries,  therefore,  must  be 
drawn  arbitrarily  or  must  be  based  on  the  presence  of  particular  species 
rather  than  the  usual  associations  of  species. 

"Counting  from  the  north,  the  Carolinian  area  is  that  in  which  the 
sassafras,  tulip-tree,  hackberry,  sycamore,  sweet  gum,  rose-magnolia,  red- 
bud,  persimmon,  and  short-leaved  pine  first  make  their  appearance. 
Chestnuts,  hickory-nuts,  hazelnuts,  and  walnuts  grow  wild  in  abundance. 
The  area  is  of  very  great  agricultural  importance. 

"Cereals  do  well  in  the  Carolinian  area,  particularly  wheat  and  corn. 
The  stigar-beet  is  an  important  crop  in  the  northern  parts,  but  fails  to 
develop  sufficient  sugar  for  profitable  culture  in  the  southern  parts." 

b.  The   Upper  Sonoran  Area. — "It  covers  most  of  the  great- plains  in 
eastern    Montana    and    Wyoming,    southwestern    South    Dakota,    western 
Nebraska,    Kansas,    Oklahoma    and    Texas,    and   eastern    Colorado   and 
New  Mexico.     In   Oregon  and  Washington  it  covers  the  plains  of  the 


PRACTICAL   STUDY  OF  PL  AN 'T  FORMATIONS.      645 

Columbia  and  the  Malheur  and  Harney  plains;  in  California  it  encircles 
the  Sacramento  and  San  Joaquin  valleys  and  forms  a  narrow  belt  along 
the  eastern  boundary  of  the  Colorado  and  Mohave  deserts;  in  Utah  it 
covers  the  Salt  Lake  and  Sevier  deserts,  in  Idaho  the  Snake  Plains,  and 
in  Nevada  and  Arizona  irregular  areas  of  suitable  elevation.  Except  in 
California  the  most  conspicuous  vegetation  of  the  Upper  Sonoran  areas 
is  the  true  sage-brush  (Artemisia  tridentata),  which,  however,  is  equally 
abundant  in  the  Transition  zone.  Several  of  the  so-called  '  grease  woods ' 
( Atriplex  confertifolia,  A.  canescens,  A.  nuttallii,  Tetradymia  canescens, 
Sarcobatus  vermiculatus,  and  Grayia  spinosa)  are  on  characteristic  soils; 
and  nut-pines  (pinon)  and  junipers  occur  here  and  there,  mostly  on  the 
mountain  slopes. 

"The  Upper  Sonoran  area,  notwithstanding  its  aridity,  is  of  consider- 
able agricultural  importance.  Fruits  and  cereals  succeed  wherever  water 
may  be  had  for  irrigation,  and  in  the  less  arid  parts  wheat,  corn,  barley, 
and  rye  yield  their  heaviest  returns.  Kaffir  corn  (a  kind  of  millet)  thrives 
without  irrigation,  particularly  on  the  great  plains,  and  alfalfa  with  irri- 
gation matures  several  crops  a  year,  though  not  so  many  as  in  the  Lower 
Sonoran." 

The  Lower  Austral  Zone. — "The  Lower  Austral  zone  occupies  the 
southern  part  of  the  United  States,  from  Chesapeake  Bay  to  the  great 
interior  valley  of  California.  It  is  interrupted  by  the  continental  divide 
in  eastern  Arizona  and  western  New  Mexico,  and  is  divided  into  an  eastern 
or  Austroriparian,  and  a  western  or  Lower  Sonoran,  area." 

a.  The  Lower  Sonoran  area. — "The  Lower  Sonoran  area  begins  with 
the  arid  region  of  Texas  in  the  neighborhood  of  latitude  98°,  and  stretches 
westerly  to  the  Rio  Grande  Valley,  in  which  it  sends  an  arm  northwest  to 
a  point  a  little  north  of  Albuquerque,  New  Mexico.  Another  arm  reaches 
up  the  valley  of  the  Pecos.  West  of  the  Rio  Grande  Valley  in  New  Mexico 
the  Lower  Sonoran  is  interrupted  by  the  continental  divide.  It  begins 
again  in  eastern  Arizona  and  sweeps  broadly  westward  below  the  high 
plateau,  covering  southern  and  western  Arizona,  the  deserts  of  southern 
Nevada  and  eastern  California,  and  the  San  Joaquin  and  Sacramento  val- 
leys. Followed  more  in  detail,  the  Lower  Sonoran  in  western  Arizona 
sends  a  narrow,  tortuous  arm  eastward  in  the  Grand  Canon  of  the  Colo- 
rado, which  expands  to  cover  the  lower  levels  of  the  Painted  Desert,  and 
another  arm  northward,  which  enters  the  extreme  southwestern  corner 
of  Utah,  where  it  is  restricted  to  the  St.  George  or  lower  Santa  Clara  Val- 
ley, and  is  of  much  agricultural  importance.  From  western  Arizona  it 
spreads  over  southern  Nevada,  pushes  northerly  into  Pahranagat  Valley, 
sends  an  arm  by  way  of  Oasis  and  Sarcobatus  valleys  all  the  way  to  the 
sink  of  the  Humboldt  and  Carson  rivers,  fills  the  whole  of  Death,  Pana- 
mint,  and  Saline  valleys  and  part  of  Owens  Valley,  and  thence  curving 


646  RELATION   TO   ENVIRONMENT. 

southwesterly  follows  the  eastern  base  of  the  Sierra  Nevada,  Techahapi, 
and  Tejon  mountains,  and  covers  the  whole  of  the  Mohave  and  Colorado 
deserts  and  all  the  rest  of  southern  California  except  the  mountains.  It 
sends  an  arm  over  most  of  the  peninsula  of  Lower  California,  and  another 
northward  over  the  San  Joaquin  and  Sacramento  valleys. 

"The  Lower  Sonoran  area  comprises  the  most  arid  deserts  of  North 
America,  and  is  characterized  by  a  flora  and  fauna  of  extreme  interest. 
Among  the  commoner  plants  are  the  creosote  bush,  mesquites,  acacias, 
cactuses,  yuccas,  and  agaves.  .  .  .  The  region,  wherever  water  may  be  had 
for  irrigation,  is  of  great  agricultural  importance,  particularly  for  fruit. 

"Raisins  and  wine  grapes,  oranges,  lemons,  olives,  prunes,  peaches, 
apricots,  English  walnuts,  and  almonds  are  among  the  important  products 
of  the  Lower  Sonoran  area,  and  the  figs  ripen  several  crops  each  year. 
Although  too  far  south  for  the  highest  development  of  cereals,  several  kinds, 
as  the  Australian  and  Sonoran  wheats,  the  red  rust-proof  oats,  and  the 
white-gourd  seed  corn,  do  well.  Cotton,  tobacco,  pyreth-um,  and  the  opium 
poppy  thrive  in  certain  localities,  and  alfalfa,  cow-peas,  and  canaigre  (a 
plant  valuable  for  tanning)  do  better  than  in  any  other  area." 

b.  The  Austroriparian  area. — "The   Austroriparian   area   occupies   the 
greater  part   of   the  South  Atlantic  and  Gulf  States.     Beginning  near  the 
mouth  of   Chesapeake    Bay  it  covers  half  or  more    than  half  of  Virginia, 
North  and  South  Carolina,  Georgia,  Florida,  Alabama,  the  whole  of  Mis- 
sissippi and  Louisiana,  eastern  Texas,  nearly  all  of  Indian  Territory,  more 
than    half  of  Arkansas,  and    parts   of   Oklahoma,    southwestern    Kansas, 
southeastern  Missouri,  southern  Illinois,  the   extreme  southwestern  corner 
of  Indiana,  and  the   bottom   lands    of  western  Kentucky  and  Tennessee. 
The  long-leaf  and  loblolly  pines,  magnolia,  and  live  oak  are  common  on 
the  uplands;  the  bald  cypress,  tupelo,  and  cane  in  the  swamps.  .  .  .  This 
is  the  zone  of  the  cotton  plant,  sugar-cane,  rice,  pecan^  and  peanut,  and 
of  the  scuppernong  grape  and  oriental  pears  (LeConte  and  Kieffer)." 

c.  The  Semitropical  or  Gulf  strip. — "The  Gulf  strip,  or  southern  part 
of  the  Austroriparian  area  reaches  from  Texas  to  southern  Florida,  covers 
a  narrow  strip  in  southern  Georgia,  and  probably  follows  the  coastal  low- 
lands northward  into  South  Carolina.     It  has  a  semitropical  climate  and 
is  the  home  of  a  number  of  plants  not  found  farther  north,  among  which 
are  the  cabbage  palmetto  and  Cuban  pine.  .  .   .  The  Gulf  strip,  though 
small  in  area,  is  of  very  great  importance  from  the  standpoint  of  agricul- 
ture and  horticulture.     It  is  the  belt  in  which  rice,  sugar-cane,  and  the 
much-prized   sea-island    cotton    are   produced    in    greatest    quantity   and 
value;  and,  as  a  fruit  belt,  has  no  competitor,  except  the  Lower  Sonoran 
areas  of  California  and  Arizona.     Bitter  oranges,  loquats,  granadillas,  figs, 
Japanese    persimmons,    pecan    nuts,    and    numerous   varieties   of   peaches 
and  grapes  thrive  here,  and  the  citrus  fruits  (oranges,  mandarins,  lemons, 


PRACTICAL  STUDY  OF  PLANT  FORMATIONS.      647 

limes,  and  shaddocks)  are  grown  successfully  in  the  warmer  parts,  par- 
ticularly in  peninsular  Florida,  but  in  the  northern  parts  have  suffered 
severely  from  frosts." 

THE  TROPICAL  REGION. — "The  tropical  region  within  the  United  States 
is  of  small  extent  and  is  restricted  to  three  widely  separated  localities — 
southern  Florida,  extreme  southeast  Texas  (along  the  lower  Rio  Grande 
and  Gulf  coast),  and  the  valley  of  the  lower  Colorado  River  in  Arizona 
and  California.  The  Florida  area  is  genuine  humid  tropical;  the  Texas 
and  Arizona-California  areas  are  dilute  arid  tropical.  Among  the  tropical 
trees  that  grow  in  southern  Florida  are  the  royal  palm,  Jamaica  dogwood, 
manchirieel,  mahogany,  and  mangrove.  .  .  .  The  extension  of  the  arid 
tropical  along  the  lower  Colorado  and  Gila  rivers  is  over  a  desert  region 
of  excessive  aridity.  .  .  .  The  flora  has  not  been  sufficiently  studied,  but  is 
characterized  by  giant  cactuses,  desert  acacias,  palo  verdes,  and  the  Wash- 
ington or  fan-leaf  palm. 

"With  irrigation  the  arid  tropical  areas  are  found  to  be  as  productive 
as  the  humid  tropical,  but  they  have  been  cultivated  so  short  a  time  that 
their  capabilities  can  only  be  inferred  from  the  circumstance  that  bananas, 
citrons,  dates,  guavas,  lemons,  loquates,  oranges,  and  Mexican  limes  do 
well  in  the  Arizona-California  arm.  No  information  is  at  hand  relating 
to  the  Texan  or  Tamaulipan  arm." 


PART   V. 

REPRESENTATIVE   FAMILIES  OF  ANGIOSPERMS. 
CHAPTER   LVIII. 

RELATION    OF    SPECIES,    GENUS,    FAMILY,    ORDER, 

ETC.* 

1133.  Species. — It  is  not  necessary  for  one  to  be  a  botanist  in 
order  to  recognize,  during  a  stroll  in  the  woods  where  the  tril- 
lium  is  flowering,  that  there  are  many  individual  plants  very 
like  each  other.  They  may  vary  in  size,  and  the  parts  may 
differ  a  little  in  form.  When  the  flowers  first  open  they  are 
usually  white,  and  in  age  they  generally  become  pinkish.  In 
some  individuals  they  are  pinkish  when  they  first  open.  Even 
with  these  variations,  which  are  trifling  in  comparison  with  the 
points  of  close  agreement,  we  recognize  the  individuals  to  be  of 
the  same  kind,  just  as  we  recognize  the  corn  plants,  grown  from 
the  seed  of  an  ear  of  corn,  as  of  the  same  kind.  Individuals  of 
the  same  kind,  in  this  sense,  form  a  species.  The  white  wake- 
robin,  then,  is  a  species. 

But  there  are  other  trilliums  which  differ  greatly  from  this  one. 
The  purple  trillium  (T.  erectum)  shown  in  fig.  537  is  very  different 


*  Chapters  XXXVIII-XLV  should  be  studied  in  connection  with  the 
following  lessons  on  families  of  the  angiosperms  (in  Chapters  LIX-LXV), 
but  especially  should  Chapters  XLII,  XLIII,  and  XLIV  be  consulted. 
See  also  Chapter  LXVI  for  the  arrangement  of  families,  orders,  etc.,  in 
classification.  See  also  ''Suggestions  for  the  teacher,"  foot  of  page  349, 
Chapter  XXXVIII;  see  also  Chapter  LVII. 

648 


CLASS  I  PICA  TION. 


649 


from  it.  So  are  a  number  of  others.  But  the  purple  trillium 
is  a  species.  It  is  made  up  of  individuals  variable,  yet  very  like 
one  another,  more  so  than 
any  one  of  them  is  like 
the  white  wake-robin. 

1134.  Genus.  — Yet   if 
we  study  all  parts  of  the 
plant,  the   perennial  root- 
stock,   the   annual    shoot, 
and  the  parts  of  the  flower, 
we    find    a    great  resem- 
blance.    In  this  respect  we  find  that 
there  are  several  species  which  possess 
the  same  general  characters.     In  other 
words,  there  is  a  relationship  between 
these  different  species,   a  relationship 
which  includes   more  than   the   indi- 
viduals  of  one  kind.      It 

includes     several     kinds. 

Obviously,  then,  this  is  a 

relationship  with  broader 

limits,  and    of    a   higher 

grade,  than  that  of  the  individuals  of  a  species.     The  grade  next 

higher  than  species  we  call  genus.     Trillium,  then,  is  a  genus. 

Briefly  the  characters  of  the  genus  trillium  are  as  follows: 

1135.  Genus  trillium.— Perianth  of  six  parts:   sepals  3,  her- 
baceous, persistent;   petals  colored.     Stamens  6  (in  two  whorls), 
anthers    opening   inward.     Ovary   3-loculed,    3~6-angled;     stig- 
mas 3,  slender,  spreading.     Herbs  with  a  stout  perennial  root- 
stock,  with  fleshy,  scale-like  leaves,  from  which  the  low  annual 
shoot  arises,  bearing  a  terminal  flower  and  3  large  netted-veined 
leaves  in  a  whorl. 

Note. — In  speaking  of  the  genus  the  present  usage  is  to  say 
trillium,  but  two  words  are  usually  employed  in  speaking  of  the 
species,  as  Trillium  grandiflorum,  T.  erectum,  etc. 

1136.  Genus  erythronium. — The    yellow    adder-tongue,    or 


Fig.  537- 
Trillium  erec- 
tum (purple 
form),  two 
plants  from  one 
rootstock. 


650 


FAMILIES   OF  ANGIOSPEKMS. 


dogtooth  violet  (Erythronium  americanum),  shown  in  fig.  538, 
is  quite  different  from  any  species  of  trillium.  It  differs  more 

from  any  of  the 
species  of  trillium 
than  they  do  from 
each  other.  The 
perianth  is, of  six 
parts,  light  yellow, 
often  spotted  near 
the  base.  Stamens 
are  6.  The  ovary 
is  obovate,  taper- 
ing at  the  base,  3- 
valved,  seeds  rather 
numerous,  and  the 
style  is  elongated. 
The  flower  stem,  or 
scape,  arises  from 
a  scaly  bulb  deep 
in  the  soil,  and  is 
sheathed  by  two  el- 
liptical -  lanceolate, 
mottled  leaves. 
Fig.  538.  The  smaller  plants 

Adder-tongue  (erythronium).     At  left  below  pistil,  and    i  fl  i 

three  stamens  opposite  three  parts  of  the  perianth.     Bulb    nave  no  HOWCr  and 

but  one  leaf,  while 

the  bulb  is  nearer  the  surface.  Each  year  new  bulbs  are  formed  at 
the  end  of  runners  from  a  parent  bulb.  These  runners  penetrate 
each  year  deeper  in  the  soil.  The  deeper  bulbs  bear  the  flower 
stems. 

1137.  Genus  lilium.— While  the  lily  differs  from  either  the 
trillium  or  erythronium,  yet  we  recognize  a  relationship  when 
we  compare  the   perianth  of  six    colored  parts,  the  6  stamens, 
and  the  3 -sided  and  long  3-loculed  ovary. 

1138.  Family  Liliaceae. — The  relationship  between  genera,  as 
between  trillium,  erythronium,  and  lilium,  brings  us  to  a  still 


CLASSIFICATION.  65! 

higher  order  of  relationship,  where  the  limits  are  broader  than  in 
the  genus.  Genera  which  are  thus  related  make  up  the  family. 
In  the  case  of  these  genera  the  family  has  been  named  after  the 
lily,  and  is  the  lily  family,  or  LiliacecB. 

1139.  Order,  class,  group. — In  like  manner  the  lily  family, 
the  iris  family,   the  amaryllis  family,   and  others  which  show 
characters  of  close  relationship  are  united  into  an  order  which 
has  broader  limits  than  the  family.     This  order  is  the  lily  order, 
or  order  Liliales.     The  various  orders  unite  to  make  up  the  class, 
and  the  classes  unite  to  form  a  group. 

1140.  Variations  in  usage  of  the  terms  class,  order,  etc.— 
Thus,  according  to  the  system  of  classification  adopted  by  some, 
the  angiosperms  form  a  group.     The  group  angiosperms  is  then 
divided  into  two  classes,  the  monocotyledones  and  dicotyledones . 
(It  should  be  remembered  that  all  systematists  do  not  agree  in 
assigning  the  same  grade  and  limits  to  the  classes,  subclasses, 
etc.     For  example,  some  treat  of  the  angiosperms  as  a  class, 
and  the  monocotyledons  and  dicotyledons  as  subclasses;    while 
others  would  divide  the  monocotyledons  and  dicotyledons  into 
classes,  instead  of  treating  each  one  as  a  class  or  as  a  subclass. 
Systematists  differ  also  in  usage  as  to  the  termination  of  the 
ordinal  name;  for 'example,  some  use  the  word  Liliales  for  Lilii- 
flora,  in  writing  of  the  order.) 

1141.  Monocotyledones. — In  the  monocotyledons  there  is  a 
single  cotyledon  on  the  embryo;    the  leaves  are  parallel  veined; 
the  parts  of  the  flower  are  usually  in  threes;   endosperm  is  usu- 
ally present  in  the  seed;  the  vascular  bundles  are  usually  closed, 
and  are  scattered  irregularly  through  the  stem  as  shown  by  a 
cross-section  of  the  stem  of  a  palm  (fig.  539),  or  by  the  arrange- 
ment of  the  bundles  in  the  corn  stem  (fig.  57).     Thus  a  single 
character  is  not  sufficient  to  show  relationship  in  the  class  (nor 
is  it  in  orders,  nor  in  many  of  the  lower  grades),  but  one  must 
use  the  sum  of  several  important  characters. 

1142.  Dicotyledones. — In   the    dicotyledons    there    are    two 
cotyledons  on  the  embryo;    the  venation  of  the  leaves  is  reticu- 
late ;  the  endosperm  is  usually  absent  in  the  seed ;  the  parts  of  the 


652 


FAMILIES   OF  ANGIOSPERMS. 


flower  are  frequently  in  fives;  the  vascular  bundles  of  the  stem 
are  generally  open  and  arranged  in  rings  around  the  stem,  as  shown 
in  the  cross-section  of  the  oak  (fig.  539).  There  are  exceptions 
to  all  the  above  characters,  and  the  sum  of  the  characters  must 
be  considered,  just  as  in  the  case  of  the  monocotyledons. 


19 


r  ni- 


A Fig.  539. 

A.  Cross-section  of  the  stem  of  an  oak  tree  thirty-seven  years  old,  showing  the 
annual  rings,  rm,  the  medullary  rays;  m,  the  pith  (medulla).  B.  Cross-section 
of  the  stem  of  a  palm  tree,  showing  the  scattered  bundles. 

1143.  Taxonomy.— This  grouping  of  plants  into  species, 
genera,  families,  etc.,  according  to  characters  and  relationships 
is  classification,  or  taxonomy. 

To  take  Trillium  grandiflorum  for  example,  its  position  in 
the  system,  if  all  the  principal  subdivisions  should  be  included 
in  the  outline,  would  be  indicated  as  follows: 
Group,  Angiosperms. 
Class,  Monocotyledones. 
Order,  Liliales. 
Family,  Liliaceae. 
Genus,  Trillium. 

Species,  grandiflorum. 

In  the  same  way  the  position  of  the  toothwort  would  be  indi- 
cated as  follows: 

Group,  Angiosperms. 
Class,  Dicotyledones. 
Order,  Papaverales. 
Family,  Cruciferae. 
Genus,  Dentaria. 
Species,  diphylla. 


CLA  SSIFICA  TION.  65  3 

But  in  giving  the  technical  name  of  the  plant  only  two  of 
these  names  are  used,  the  genus  and  species,  so  that  for  the 
toothwort  we  say  Dentaria  diphylla,  and  for  the  white  wake- 
robin  we  say  Trillium  grandiflorum. 

1144.  Kingdom  and  Subkingdom. — Organic  beings  form  alto- 
gether two  kingdoms,  the  Animal  Kingdom  and  the  Plant  King- 
dom. The  plant  Kingdom  is  then  divided  into  a  number  of 
subkingdoms  as  follows:  ist,  Subkingdom  Thallophyta,  the 
thallus  plants,  including  the  Algae  and  Fungi;  2d,  Subkingdom 
Bryophyta,  the  moss-like  plants,  including  the  Liverworts  and 
Mosses;  3d,  Subkingdom  Pteridophyta,  the  fern-like  plants, 
including  Ferns,  Lycopods,  Equisetum,  Isoetes,  etc.;  4th,  Sub- 
kingdom  Spermatophyta,  the  seed-plants,  including  Gymno- 
sperms  and  Angiosperms.  Subkingdoms  are  divided  into  groups 
of  lower  order  down  to  the  classes.  So  there  are  subclasses, 
subfamilies  or  tribes,  subgenera,  and  even  subspecies.  But 
taking  the  principal  taxonomic  divisions  from  the  greater  to  the 
lesser  rank,  the  order  would  be  as  follows: 
Plant  Kingdom. 

Subkingdom,  Spermatophyta. 

Group  (not  used  in  a  definite  sense). 
Class,  Gymnospermae. 
Order,  Pinales. 
Family,  Pinaceae. 
Genus,  Pinus. 

Species,  strobus,  or,  in  full. 
Pinus  strobus,  the  white  pine. 


CHAPTER  LIX. 

MONOCOTYLEDONS. 

Topic  I :  Monocotyledons  with  conspicuous  petals 
and  regular  flowers. 

ORDEB   LILIALES. 

1145.  Lesson  I.  The  lily  family  (Liliaceae).— Trillium,  which 
we  employed  as  a  representative  of  the  monocotyledons  in  the 
morphology  of  the  angiosperms,  serves  as  one  type  of  the  lily 
family.     An   exercise   is   added   here   on   the   "yellow   adder's- 
tongue"  for  those  who  wish  to  study  more  than  one  example  of 
the  order.     There  is  an  abundance  of  material  from  the  mem- 
bers of  the  family  if  the  teacher  desires  to  extend  further  the 
exercises  on  the  Liliaceae. 

Yellow  adder 's-tongue   (Erythronium  americanum). 

SUGGESTIONS   FOR   STUDY   OF   THE  YELLOW  ADDER'S-TONGUE. 

1146.  Entire  plant. — Observe  the  bulb  from  which  the  flowering  scape 
arises;    the  small  scale-like  leaves  overlapping  it;    the  two  large  spotted 
leaves  on  plants  which  have  the  flower.     In  the  case  of  the  non -flowering 
plants  observe  that  there  is  only  one  large  leaf.     If  an  opportunity  affords 
for  an  excursion  in  the  woods  where  the  plant  grows,  see  if  you  can  deter- 
mine how  the  bulbs  are  formed  at  the  ends  of  the  "runners."     As  to  depth 
in  the  soil  compare  the  bulbs  of  the  flowering  and  non-flowering  plants. 

Inflorescence. — The  inflorescence  is  determinate,  and  consists  of  a  single 
terminal  nodding  flower  on  a  scape. 

Flower. — Beginning  with  the  outer  whorl  of  members  of  the  flower  deter- 
mine the  number  of  members  in  each  whorl,  as  well  as  their  form,  relation 
to  each  other,  and  the  relation  of  the  different  sets  among  themselves. 

654 


MONOCOTYLEDONS:   LILIACE^E.  655 

Sketch  a  member  of  the  calyx,  corolla,  and  androecium.  Sketch  the 
pistil,  naming  the  parts.  Make  a  section  of  tfce  pistil  (preferably  one  in 
which  the  seeds  are  nearly  mature)  and  determine  the  number  of  carpels 
united  to  form  it.  How  are  the  number  of  carpels  manifested  in  the  stigma? 

Construct  a  floral  diagram  to  show  the  relation  and  number  of  the  different 
members  of  the  flower. 

The  flower  of  the  adder's-tongue  is  complete,  because  it  possesses  all  the 
floral  sets.  It  is  perfect,  because  it  possesses  both  the  androecium  and 
gyncecium.  It  is  regular,  because  all  the  members  of  the  calyx,  as  well 
as  those  of  the  corolla,  are  of  equal  size. 

1147.  Other  examples  of  the  lily  family.— The  lily  family  is 
a  large  one.  Another  example  is  found  in  the  "Solomon's- 
seal,"  with  its  elongated,  perennial  rootstock,  the  scars  formed 
by  the  falling  away  of  each  annual  shoot  resembling  a  seal.  The 
onion,  smilax,  asparagus,  lily-of-the-valley,  etc.,  are  members  of 
the  lily  family.  The  parts  of  the  flower  are  usually  in  threes, 
though  there  is  an  exception  in  the  genus  Unijolium,  where  the 
parts  are  in  twos.  A  remarkable  exception  occurs  sometimes  in 
Trillium  grandiflorum,  where  the  flower  is  abnormal  and  the 
parts  are  in  twos. 

OUTDOOR  OBSERVATIONS  ON  SOME  OF  THE  LILIACE^E. 

If  the  study  of  the  plant  families  is  carried  on  during  the  spring, 
excursions  should  be  made,  if  possible,  to  the  fields  and  woods 
at  opportune  times  for  the  purpose  of  studying  some  of  the 
plants  in  their  natural  surroundings.  The  short  studies  given 
here  will  serve  to  indicate  some  of  the  observations  that  can  be 
made  during  these  excursions. 

Some  of  the  early  spring  flowers  like  trillium  and  erythronium 
are  formed  the  previous  year,  and  are  nearly  or  quite  mature  in 
the  autumn.  The  flower-bud  is,  of  course,  at  this  time  unfolded. 
The  stem  which  bears  the  flower  is  very  short,  so  that  the  flower- 
bud  is  covered  by  leaf-mold  and  soft  humus  during  the  winter. 
If  possible  one  should  examine  plants  of  trillium  at  intervals  of 
three  or  four  weeks  during  the  spring,  summer,  and  autumn. 
The  young  flower  begins  to  form  in  June  and  July,  and  by  autumn 


MONOCOTYLEDONS:    LTLTACEJE. 


657 


its  parts  are  all  formed.  Sometimes  in  places  well  exposed  to 
the  sun  the  pollen  is  already  developed  in  the  autumn,  while  in 
other  cases  it  is  formed  during  warm  days  in  the  winter  or  in 
early  spring,  always  before  the  flower  opens  above  ground.  In 
connection  with  these  studies  one  should  consult  Parts  III  and 
IV.  Relation  of  Plants  to  Environment,  Ecology. 


Topic  II:   Monocotyledons  with  a  glume  subtending 
the  flower  (Glumiflorse). 

ORDER  GRAMINALES. 

1148.    Lesson  II.     Grass  family  (Gramineae).     Oat. — As  a 

representative  of  the  grass  family  (gramineae)  one  may  take  the 


Fig.  541 
Spikelet    of 


Fig.  542. 
One  glume  re- 


Fig.  543- 

Flower    opened 

oat     showing    moved  "showing    showing  two  palets, 
two  glumes.         fertile  flower.          three    stamens,    and     of  flower,  a,  axis 
two  lodicules  at  base 
of  pistil. 


Fig.  544- 

Section     show-     ing  the  upper 
ng    ground  plan     palet  behind, 
and   the   two 
lodicules      in 
front. 


oat  plant,  which  is  widely  cultivated,  and  also  can  be  grown 
readily  in  gardens,  or  perhaps  in  small  quantities  in  greenhouses 
in  order  to  have  material  in  a  fresh  condition  for  study.  Or  we 
may  have  recourse  to  material  preserved  in  alcohol  for  the  dis- 
section of  the  flower.  The  plants  grow  usually  in  stools;  the 


658 


FAMILIES   OF  ANGIOSPERMS. 


stem  is  cylindrical,  and  marked  by  distinct  nodes,  as  in  the  corn 
plant.  The  leaves  possess  a  sheath  and  blade.  The  flowers 
form  a  loose  head  of  a  type  known  as  a  panicle.  Each  little 
cluster  as  shown  in  fig.  541  is  a  spikelet,  and  consists  usually 
here  of  one  or  two  fertile  flowers  below  and  one  or  two  unde- 
veloped flowers  above.  We  see  that  there  are  several  series 
of  overlapping  scales.  The  two  lower  ones  are  "glumes," 
and  because  they  bear  no  flower  in  their  axils  are  empty  glumes. 
Within  these  empty  glumes  and  a  little  higher  on  the  axis  of  the 
spike  is  seen  a  boat-shaped  body,  formed  of  a  scale,  the  margins 
of  which  are  folded  around  the  flowers  within,,  and  the  edges 
inrolled  in  a  peculiar  manner  when  mature.  From  the  back  of 
this  glume  is  usually  borne  an  awn.  If  we  carefully  remove 
this  scale,  the  "flower  glume,"  we  find  that  there  is  another 
scale  on  the  opposite  (inner)  side,  and  much  smaller.  This  is 
the"palet." 

1149.  Next  above  this  we  have  the  flower,  and  the  most  prom- 
inent part  of  the  flower,  as  we  see,  is  the  short  pistil  with  the  two 
plume-like  styles,  and  the  three  stamens  at  fig.  543.     But  if  we 

are  careful  in  the  dissection 
of  the  parts  we  shall  see,  on 
looking  close  below  the  pis- 
til on  the  side  of  the  flower- 
ing glume,  that  there  are 
two  minute  scales  (fig.  545). 
These  are  what  are  termed 
the  lodicules,  considered  by 
some  to  be  merely  bracts, 
by  others  to  represent  a  pe- 
rianth, that  is  two  of  the 
sepals,  the  third  sepal  hav- 
ing entirely  aborted.  Ru- 
diments of  this  third  sepal 
GI,  glumes;  B,  are  present  in  some  of  the 
gramineae. 

1150.  To  the  gramineae  belong  also  the  wheat,  barley,  corn 


Fig.  546. 

Diagram    o  f  oat  spikelet. 
palets;  A,  abortive  flower. 


MONOCOTYLEDONS:   LILIACE&.  659 

the  grasses,  etc.  The  gramineae,  while  belonging  to  the  class 
monocotyledons,  are  less  closely  allied  to  the  other  families  of 
the  class  than  these  families  are  to  each  other.  For  this  reason 
they  are  regarded  as  a  very  natural  group. 


SUGGESTIONS  FOR  THE  STUDY  OF  THE  CORN. 

1151.  The  corn  (Zea  mays). — The  corn  or  wheat  plant  may  be  studied 
as  an  alternate  for  the  oat  plant. 

The  corn  plant. — Describe  the  entire  plant;  the  underground  roots; 
the  aerial  roots  in  the  case  of  mature  plants;  the  nodes  and  internodes  of 
the  stem;  the  leaves.  Determine  the  arrangement  of  the  leaves;  the  parts 
of  the  leaf  (blade,  sheath;  is  there  a  ligule,  a  membranous  appendage  at 
the  junction  of  the  blade  and  sheath,  present?).  Sketch  a  leaf  showing 
all  the  parts.  Sketch  an  entire  plant  to  show  details.  (See  Chapter  X 
for  structure  of  seed,  and  germination.) 

The  staminate  inflorescence  (the  " tassel")  forms  a  terminal  panicle 
on  the  stem,  composed  of  several  spikes  which  branch  from  the  axis. 
Note  the  numerous  spikelets  on  each  spike.  Determine  the  number  of 
spikelets  at  each  joint  of  the  rachis  (axis  of  the  spike).  Separate  the 
parts  of  a  spikelet,  and  sketch  to  show  the  parts  of  a  flower  as  in  the 
oat  shown  in  figs.  545  and  546.  Make  a  diagram  to  show  the  ground  plan 
of  the  flower. 

The  pistillate  inflorescence  (the  ear  of  corn).  This  occurs  in  the  axil 
of  the  leaves  at  the  joints  of  the  stem.  The  spikes  of  each  leaf-axil  are 
grown  together  into  a  thickened  axis  ("cob"),  forming  the  "ear"  of  corn 
which  is  covered  by  the  numerous  leaf-like  bracts  ("husks")  arising  from 
its  base.  The  styles,  each  attached  to  the  ovary,  emerge  from  between  the 
ends  of  the  bracts  in  a  silky  tuft. 

Sketch  a  cross-section  of  an  ear  showing  the  arrangement  of  the  ovaries 
or  grains  of  corn  on  the  axis  (cob).  Remove  some  of  the  ovules  (or  grains 
of  mature  corn)  and  note  the  scale-like  bracts  at  the  base  of  each.  (In 
some  varieties  of  corn  these  scale-like  bracts  are  larger  and  enclose  the 
grain,  as  in  the  oat  or  barley. 

Material. — Entire  corn  plants  at  maturity  (may  be  preserved  dry); 
young  "ears"  of  corn  at  time  the  silk  is  formed  (may  be  preserved  in  alco- 
hol or  dry);  the  "tassel,"  at  the  time  of  flowering  (some  of  the  material 
should  be  preserved  in  alcohol  or  formalin);  ripe  ears  of  corn  with  the 
"husks"  (dry). 

1152.  Lesson  III.     The  sedge  family  (Cyperacese).     Carex. — As  an  ex- 
ample of  the  sedges  a  species  of  the  genus  carex  may  be  studied.     If  plants 


66o 


FAMILIES   OF  ANGIOSPERMS. 


of  Carex  lupulina  are  taken  from  the  soil  carefully,  we  find  that  there  is  an 
underground   stem  or  rootstock  which  each  year    grows    a    few    inches, 

forms  new  attachments  by 
roots  to  the  soil,  and  thus 
the  plant  may  spread  from 
year  to  year.  This  under- 
ground stem,  as  seen,  has 
only  scaly  leaves.  The  up- 
right stems*  reach  a  height 
of  two  to  three  feet,  and  are 
prominently  three-angled,  as 
are  most  of  the  species  of 
this  large  genus.  The  leaves 
are  three-ranked,  and  con- 
sist of  a  long  sheathing  base 
and  a  long  narrow  blade. 
The  flowers,  as  we  see,  are 


Fig.  547- 

\\l\\tt  Flowers  of  Carex  lupulina;  staminate  flower-spike  above,  three 

//////  pistillate  flower-spikes  below.       Details  of  pistillate  and  stami- 

nate flowers  shown  at  the  right. 

clustered  at  the  end  of  the  stem,  or  sometimes  additional  ones  arise  in 
the  axils  of  the  leaves  lower  down  on  the  stem.  The  staminate  flowers 
form  a  slender,  short  spike,  terminating  the  stem,  while  the  pistillate  flowers 
form  several  spikes  arising  as  branches.  The  flowers  are  very  much 
reduced  here,  and  each  of  the  pistillate  flowers  consists  of  one  pistil  which 
is  surrounded  by  a  flask-shaped  scale,  the  perigynium.  These  perigynia 
can  be  distinctly  seen  upon  the  spike.  At  the  apex  of  the  perigynia  the 


MONOCOTYLEDONS:  LILIACEJE. 


66 1 


three  styles  emerge.     Just  below  each  perigynium  is  a  slender  scale,  the 
primary  bract,  from  the  axil  of  which  the  pistillate  flower  arises. 


Fig.  548. 
Two  carex  flowers. 


Fig.  549- 
Pistil  of  carex. 


Fig.  550. 
Section  of  pistil. 


For  the  study  of  the  flowers  one  must  select  material  at  the  time  the  male 
flowers  are  in  bloom.  In  fig.  551  is  represented  a  portion  of  the  staminate 
spike  of  Carex  laxiflora.  As 
seen  here  each  staminate  flower 
consists  of  three  stamens. 
These  stamens  arise  in  the 
axil  of  a  bract.  Figure  548 
represents  a  portion  of  the 
pistillate  spike  of  the  same 
species  at  the  time  of  flower- 
ing The  fact  that  the  parts, 
or  members,  of  the  flower  are 
in  threes  suggests  that  there 
may  be  some  relationship  be- 
tween the  carex  and  the  mono- 
cotyledons already  studied,  even 
though  each  flower  has  be- 
come so  reduced  in  the  number 
of  its  members. 

1153.  In   the   bulrush   (scir- 

pus),    another    genus    of    this  Fig.  5SI. 

family,  the  flowers   are  perfect  Two  male  flowers  of  Carex  laxiflora. 

and  complete  (having  all  parts  of  the  flower),  with  the  parts  in  threes  or 
some  multiple  of  three.  Here  there  is  a  more  obvious  resemblance  to  the 
monocotyledenous  type. 


CHAPTER  LX. 

MONOCOTYLEDONS  CONCLUDED. 

Topic  III.  Monocotyledons  with  Flowers  on  a 
Spadix. 

ORDER   ARALES. 

1154.  Lesson  IV.  The  arum  family  (Aracese).— This  family 
is   well   represented   by   several  plants.     The   skunk's   cabbage 
(Spathyema  fcetida)  illustrated  in  figs.  458-460  is  an  interest- 
ing example.     The  flowers  are  closely  crowded  around  a  thick 
stem  axis.     Such  an  arrangement  of  flowers  forms  a  "spadix" 
The  spadix  is  partly  enclosed  in  a  large  bract,  the  "spathe" 
The  sepals  and  stamens  are  four  in  number,  and  the  pistil  has  a 
four-angled  style.     The  coralla  is  wanting.     (See  Chapter  XLIII 
for  farther  characters  of  the  flower.) 

1155.  The  " jack-in-the-pulpit,"  also  called  "Indian  turnip" 
(Arisaema  triphyllum),  shown  in  fig.  461,  the  water-arum  (Calla 
palustris),  and  the  sweet  flag  (Acorus  calamus)  are  members  of 
this  family,  as  also  are  the  callas  and  caladiums  grown  in  con- 
servatories.    The  parts  of  several  of  the  species  of  this  family, 
especially  the  corm  of  the  Indian  turnip,  are  very  acrid  to  the 
taste.     The  floral  parts  are  more  or  less  reduced. 

DESCRIPTION  OF  THE  INDIAN  TURNIP. 

Indian  turnip. — The  "Indian  turnip,"  or  "  jack-in-the-pulpit" 
(Arisaema  triphyllum),  loves  the  cool,  shady,  rich,  alluvial  soil 

662 


MONOCOTYLEDONS:   ARALES.  663 

of  low  grounds,  or  along  streams,  or  on  moist  hillsides.  A 
group  of  the  jacks  is  shown  in  fig.  461  as  they  occur  in  the 
rich  soil  on  dripping  rocks  in  one  of  our  glens.  The  thin,  strap- 
shaped  spathe,  unfolded  at  its  base,  bends  gracefully  over  the 
spadix,  the  sterile  end  of  which  stands  solitary  in  the  pulpit 
thus  formed.  The  flowers  are  very  much  reduced,  i.e.,  the 
number  of  members  in  the  sets  is  reduced  so  that  they  do  not 
appear  in  threes  as  in  the  typical  monocotyledons.  Some  of 
the  members  are  also  often  reduced  in  size  or  are  rudimentary. 
The  plants  are  "dimorphic"  usually. 

Female  plants.— The  large  plants  usually  bear  the  pistillate 
flowers,  which  are  clustered  around  the  base  of  the  spadix, 
each  flower  consisting  of  a  single  pistil,  oval  in  form,  terminating 
in  a  brush-like  stigma.  The  stigma  consists  of  numerous  spread- 
ing, delicate  hairs.  The  open  cavity  of  the  short  style  is  hairy 
also,  and  a  brush  of  hairs  extends  into  the  cavity  of  the  ovary. 
Into  this  brush  of  internal  hairs  the  necks  of  the  several  ovules 
crowd  their  way  to  the  base  of  the  style  near  its  opening.  Even 
when  the  stigma  is  not  pollinated  the  ovary  continues  to  grow 
in  size,  and  the  stigmatic  brush  remains  fresh  for  a  long  time. 

Male  plants. — Excepting  some  of  the  intermediate  sizes,  one 
can  usually  select  on  sight  the  male  and  female  plants.  The 
smaller  ones  which  have  a  spathe  are  nearly  all  male  and  bear 
a  single  leaf,  though  a  few  have  two  leaves.  The  male  flowers 
are  also  clustered  at  the  base  of  the  spadix,  and  are  very  much 
reduced.  Each  flower  consists  only  of  stamens,  and  singularly 
the  stamens  of  each  flower  are  joined  into  one  compound  stamen, 
the  anther-sacs  forming  rounded  lobes  at  the  end  of  the  short 
consolidated  filaments. 

The  female  plants  require  more  food  than  the  male  plants. — 
In  some  plants  both  male  and  female  flowers  occur  on  a  single 
spadix,  the  lower  flowers  being  female,  while  the  upper  ones 
are  male.  The  larger  plants  are  nearly  all  female,  and  many, 
though  not  all,  bear  two  leaves.  In  this  dimorphism  of  the 
plant  there  is  a  division  of  labor  apportioned  to  the  destiny 
and  needs  of  each,  and  in  direct  correspondence  with  the  capacity 


664  FAMILIES   OF  ANGIOSPERMS. 

to  supply  nutriment.  The  staminate  flowers,  being  short-lived, 
need  a  comparatively  small  amount  of  nutriment,  and  after 
the  escape  of  the  pollen  (dehiscence  of  the  anthers)  the  spathe 
dies,  while  the  leaf  remains  green  to  assimilate  food  for  growth 
of  the  fleshy  short  stem  (corm),  where  also  is  stored  nutriment 
for  the  growth  in  the  autumn  and  spring  when  the  leaf  is  dead. 
The  female  plants  have  more  work  to  do  in  providing  for  the 
growth  of  the  embryo  and  seed,  in  addition  to  the  growth  of 
the  corm  and  next  season's  flower.  The  smaller  female  plants 
thus  sometimes  so  exhaust  themselves  in  seed-bearing  that  the 
corm  becomes  small,  and  the  follpwing  season  the  plant  is  reduced 
to  a  male  one. 

Growth  and  death  of  the  corm. — The  new  roots  each  year 
arise  from  the  upper  part  of  the  corm.  The  stored  substances 
in  the  base  of  the  corm  are  used  in  the  early  season's  growth, 
and  the  old  tissue  sloughs  off  as  the  new  corm  is  formed  above 
upon  its  remains. 

SUGGESTIONS  FOR  STUDY  OF  THE  INDIAN  TURNIP. 

Staminate  plants  (sometimes  called  male  plants). — Sketch  an  entire 
plant  showing  the  corm  (the  thickened  perennial  stem),  the  annual  shoot 
with  leaves  and  spathe.  Cut  away  one  side  of  the  spathe  to  expose  the 
long  compact  cluster  (spadix)  of  staminate  flowers  within.  Sketch  the 
spadix,  showing  the  mass  of  stamens  as  well  as  the  sterile  part  of  the  shoot 
above.  Dissect  off  from  the  axis  several  of  the  stamens.  Note  that  the 
filament  is  very  short,  and  that  the  anther  is  irregularly  lobed. 

The  pistillate  plants  (sometimes  called  female  plants). — Compare  with 
the  staminate  plant.  How  many  leaves  are  there?  Is  the  number  of 
leaves  constant  on  all  the  pistillate  plants  ?  Cut  away  one  side  of  the  spathe 
and  expose  the  spadix  of  pistillate  flowers.  Sketch.  Observe  that  each 
flower  consists  of  a  single  flask-shaped  pistil,  and  that  these  are  packed 
closely  together.  Note  the  delicate  brush-like  stigma.  Search  for  plants 
which  show  both  stamens  and  pistils  on  the  same  spadix.  Where  both 
kinds  of  flowers  are  present  on  the  same  spadix,  on  what  part  of  the  spadix 
does  each  kind  appear  ?  On  the  corm  of  different  plants  search  for  lateral 
buds,  which  are  young  plants.  Observe  that  they  usually  arise  on  directly 
opposite  sides  of  the  corm;  that  they  easily  become  freed  from  the  old 
corms;  that  they  are  young  corms.  Do  they  arise  in  the  axils  of  the  leaves 
or  scale  leaves  which  have  fallen  away? 


MONOCOTYLEDONS:    ORCHIDALES. 


665 


Cut  off  a  portion  of  the  corm.  Do  not  eat  any  portion,  but  touch  the 
tongue  to  the  cut  surface.  The  flesh  of  the  corm  is  very  acrid. 

Material. — Freshly  collected  plants  should  be  used,  the  entire  plant; 
small  ones  as  well  as  large  ones. 

1156.  Related    to    the    arum   family    are    the    "duckweeds." 
Among  the  members  of  this  family  are  the  most  diminutive  of 
the  flowering  plants,  as  well  as  the  most  reduced  floral  structures. 
(For  description  and  illustration  of  three  of  these  duckweeds, 
see  Chapter  III.) 

Other  related  families  are  the  cat-tails  and  palms.  In  the 
latter  the  spathe  and  spadix  are  of  enormous  size.  The  cocoa- 
nut  is  the  fruit  of  the  cocoanut  palm. 

Topic  IV:    Monocotyledons  with  large  petals  and 
irregular  flowers. 

ORDEK  OECHIDALES. 

1157.  Lesson    V.     The    orchid    family     (Orchidaceae). — In   the   orchids 
are  found  the  most  striking  departures  from  the  arrangement  of  the  flower 
which    we    found    in    the 

simpler  monocotyledons. 
An  example  of  this  is  seen 
in  the  lady- slipper  (Cypri- 
pedium,  shown  in  fig.  467). 
The  ovary  appears  to  be 
below  the  calyx  and  co- 
rolla. This  is  brought 
about  by  the  adhesion  of 
the  lower  pa't  of  the 
calyx  to  the  wall  of  the 
ovary.  The  ova~y  then 
is  inferior,  while  the 
calyx  and  corolla  are 
epigynoi:s.  The  stamens 
are  united  with  the  style 
by  adhesion,  two  lateral 

perfect  ones  and  one  upper  imperfect  one.  The  stamens  are  thus  gynan- 
drou*.  The  sepals  and  petals  are  each  three  in  number.  One  of  the  petals, 
the  "slipper,"  is  large,  nearly  horizontal,  and  forms  the  "lip"  or  "label- 
lum"  of  the  orchid  flower.  The  labellum  is  the  platform  or  landing-place 
for  the  insect  in  cross-pollination  (see  Chapter  XLIII,  Pollination).  Above 


Fig.  552. 

Flower  of  an  orchid  (Epipactis),  the  inferior  ovary 
twisted  as  in  all  orchids  so  as  to  bring  the  upper  part 
of  the  flower  below. 


666 


FAMILIES   OF  ANGIOSPERMS. 


the  labellum  stands  one  of  the  sepals  more  showy  than  the  others,  the 
"banner."  The  two  lateral  "strings"  of  the  slipper  are  the  two  other 
petals.  The  stamens  are  still  more  reduced  in  some  other  genera,  while 
in  several  tropical  orchids  three  normal  stamens  are  present. 

There  are  thus  four  striking  modifications  of  the  orchid  flower:  ist,  the 
flower  is  irregular  (the  parts  of  a  set  are  different  in  size  and  shape);  2d, 
adnation  of  all  parts  with  the  pistil;  3d,  reduction  and  suppression  of  the 
stamens;  4th,  the  ovary  is  twisted  half-way  around  so  that  the  posterior 


Fig.  553- 

Diagrams  of  orchid  flowers.     A ,  the  usual 
type;  B,  of  cypripedium.     (Vines.) 


Fig-  554- 

Diagram  of  flower 
of  canna. 


side  of  the  flower  becomes  anterior.  Floral  diagrams  in  fig.  553  show 
the  position  of  the  stamens  in  two  distinct  types.  The  number  of  orchid 
species  is  very  large,  and  the  majority  are  found  in  tropical  countries. 

Related  to  the  orchids  are  the  iris  family,  in  which  the  stigma  is  expanded 
into  the  form  of  a  petal,  and  the  canna  family.  In  the  canna  the  flower 
is  irregular  (see  figs.  470,  471)  and  the  ovary  is  inferior.  (See  Chapter 
XLIII,  on  pollination,  for  description  of  the  canna  flower.) 


CHAPTER  LXI. 

DICOTYLEDONS. 

Topic  V:  Dicotyledons  with  distinct  petals,  flowers 
in  catkins,  or  aments;  often  degenerate. 

ORDER  SALICALES. 

1158.  Lesson  VI.  The  willow  family  (Salicaceae).— The  wil- 
lows represent  a  very  interesting  group  of  plants  in  which  the 
flowers   are   greatly  reduced.     The   flowers   are   crowded  on   a 
more  or  less  elongated  axis  forming  a  catkin,  or  ament.     The 
ament    is    characteristic    of    several    other    families    also.     The 
willows  are  dioecious,  the  male  and  female  catkins  being  borne 
on  different  plants.     The  catkins  appear  like  great  masses  of 
either  stamens  or  pistils.     But  if  we  dissect  off  several  of  the 
flowers  from  the  axis,  we  find  that  there  are  many  flowers,  each 
one  subtended  by  a  small  bract.     In  the  male  or  "sterile"  cat- 
kins the  flower  consists  of  two  to  eight  stamens,  while  in  the 
female  or  "fertile"  catkins  the  flower  consists  of  a  single  pistil. 
The  poplars  and  willows  make  up  the  willow  family. 

SUGGESTIONS  FOR  STUDY  OF  THE  WILLOW. 

1159.  The  willow  (Salix  discolor). 

The  leafy  shoot. — Determine  the  arrangement  of  the  leaves  of  the  willow; 
sketch  a  leaf  showing  its  form,  the  character  of  the  margin  and  of  the  vena- 
tion. If  different  willows  are  at  hand,  compare  the  color  of  the  twigs,  as 
well  as  the  character  of  the  twigs  as  to  brittleness  or  litheness. 

The  inflorescence. — What  is  the  kind  of  inflorescence?  Are  both  kinds 
of  flowers  borne  on  the  same  ament  (catkin)  or  on  different  aments? 

The  staminate  catkins. — Determine  what  constitutes  a  flower  by  dis- 
secting some  of  them  off  from  the  axis  of  the  catkin.  What  parts  of  the 

667 


668 


FAMILIES  OF  ANGIOSPERMS. 


flower  are  present?  How  many  stamens  in  a  flower?  If  a  hand  lens  is 
convenient,  use  it  in  making  out  the  form  of  the  parts.  Sketch  a  flower  in 
its  position  on  the  axis  of  the  catkin,  showing  also  the  bract  at  the  base  of 
the  flower.  Describe  the  character  of  the  bract  as  seen  under  the  lens. 

The  pistillate  catkin. — What  parts  of  the  flower  are  present?     Compare 
with  the  staminate  flower.     Sketch  a  pistillate  flower  with  the  subtending 


Fig.  555- 
Spray  of  willow  leaves,  pistillate  and  staminate  catkins  (Salix  discolor). 

bract  to  show  the  form  of  the  ovary,  with  the  divided  stigma.     Is  the  pistil 
jSile  or  stalked?     How  many  carpels  make  up  the  pistil?     Is  there  a 
small  gland  (nectary)  present  near  the  base  of  the  ovary  which  represents 
the  perianth?     Is  there  a  nectary  on  the  staminate  flower? 

The  fruit. — Examine  ripe  pods  of  the  willow.  Determine  what  parts 
of  the  flower  unite  to  form  the  fruit.  What  difference  between  a  fruit  and 
seed  in  the  willow?  What  means  is  provided  for  the  dissemination  of  the 
seeds? 

Field  observations  on  the  willows.— At  what  time  do  the  catkins  of  the 
willow  appear?  Do  they  flower  before  the  leaves  appear?  At  time  of 
flowering  note  the  character  and  abundance  of  the  pollen  from  the  stamens. 
Is  it  in  the  form  of  "dust,"  or  is  it  adhesive?  How  are  the  willows 
pollinated  ?  Do  insects  visit  the  willow  flower  ?  Are  willows  easily  prop- 
agated by  shoots  ?  What  happens  if  a  willow  branch  is  stuck  into  damp 
soils;  when  it  is  left  in  the  water  for  some  time? 


DICO  T  YLED  ONS  :    FA  G  A  LES. 


669 


Material. — Shoots  of  the  willow,  some  with  leaves,  some  with  the  catkins 
(the  two  kinds  of  catkins  occur  on  different  plants).  If  material  cannot  be 
obtained  fresh  when  wanted  for  study,  the  leafy  shoots  may  be  preserved 
dry,  and  the  catkins  in  alcohol  or  formalin,  or  dry.  Ripe  fruit  should 
also  be  at  hand;  this  may  be  preserved  dry. 

ORDER  FAGALES. 

1160.  Lesson  VII.  The  oak  family  (Cupuliferse).— A  small 
branch  of  the  red  oak  (Quercus  rubra)  is  illustrated  in  fig.  556. 
This  is  one  of  the  rarer  oaks,  and  is  difficult  for  the  beginner  to 


Fig.  556. 

Spray  of  oak  leaves  and  flowers.      Below  at  right  is  staminate  flower,  at  left 
pistillate  flower. 

distinguish  from  the  scarlet  oak.     The  white  oak  is  perhaps  in 
some  localities  a  more  convenient  species  to  study.     But  for  the 


670 


FAMILIES   OF  ANGIOSPERMS. 


general  description  here  the  red  oak  will  serve  the  purpose.     Just 
as  the  leaves  are  expanding  in  the  spring,  the  delicate  sprays  of 

pendulous  male  catkins 
form  beautiful  objects.  The 
petals  are 
wanting  in  the 
flower,  and 
the  sepals 
form  a  united 
calyx,  with 
several  lobes, 
that  is,  the 
parts  of  the 
calyx  are  co- 

VIS-  557- 

Branch  of  the  butter- 
nut. Cluster  of  female 
flowers  at  the  top,  show- 
ing the  two  styles  of 
each  pistil,  catkins  be- 
low. 

herent.  In  the  male  flowers  the  calyx  is  bell-shaped 
and  deeply  lobed.  The  pendant  stamens,  variable 
in  number,  just  reach  below  its  margin.  The  pistil- 
late or  female  flowers  are  not  borne  in  catkins,  but 
stand  on  short  stalks,  either  singly  or  a  few  in  a 
cluster.  The  calyx  here  is  urn-shaped  with  short  lobes.  The 
ovary  consists  of  three  united  (coherent)  carpels,  and  there  are 
three  stigmas.  Only  one  seed  is  developed  in  the  ovary,  and  the 
fruit  is  an  acorn.  The  numerous  scales  at  the  base  of  the  ovary 
form  a  scaly  involucre,  the  cup. 

The  beech,  chestnut,  and  oak  are  members  of  the  oak  family. 

The  following  additional  families  among  the  ament-bearers 
are  represented  in  this  country:  the  birch  family  (birch,  alder), 
the  hazelnut  family  (hazelnut,  hornbeam,  etc.),  walnut  family 
(hickory,  walnut),  and  the  sweet-gale  family  (myrica). 


DICOTYLEDONS:  FAG  ALES.  67 


SUGGESTIONS  FOR  STUDY  OF  THE  OAK. 

1161.  The  oak. — (The  white  oak  or  any  common  one  in  the  neighbor- 
hood.) 

The  leaves. — Determine  the  arrangement  of  the  leaves  on  the  shoot. 
Sketch  a  leaf  showing  the  form,  outline,  and  venation.  Compare  the 
young  leaves  with  the  old  ones  as  to  texture,  surface  characters,  etc. 

The  inflorescence. — What  is  the  kind  of  inflorescence?  Are  both  kinds 
of  flowers  in  the  same  inflorescence  or  in  different  inflorescences? 

The  staminate  inflorescence. — Note  the  cluster  of  staminate  aments. 
Determine  a  single  flower  and  sketch  it  to  show  the  parts.  What  parts  of 
the  flower  are  present  ?  Determine  the  number  of  parts  of  each  set  present. 

The  pistillate  inflorescence. — How  does  it  differ  from  the  staminate  in- 
florescence? Sketch  a  pistillate  flower,  showing  the  parts.  What  parts 
of  the  flower  are  present? 

The  fruit  (an  acorn  with  the  cup). — Sketch  an  acorn  in  the  "cup." 
What  is  the  homology  of  the  cup — i.e.,  to  what  part  or  series  of  members 
of  the  plant  does  it  belong?  Could  the  pistillate  flower  of  the  ancestors 
of  the  oak  have  been  in  the  form  of  aments,  and  if  so,  could  the  cup  of  the 
acorn  represent  the  degraded  and  consolidated  ament?  If  so,  what  part 
of  the  ament  would  now  be  represented  in  the  cup?  (It  has  also  been 
suggested  that  the  scales  of  the  involucre  which  makes  up  the  cup  are 
adventitious  growths  accompanying  the  development  of  the  fruit.)  See 
Chapter  XLIV. 

(If  the  acorn  has  not  been  studied  under  the  paragraph  dealing  with 
seeds  and  fruits,  and  if  there  is  time  now,  remove  the  wall  of  the  acorn 
and  determine  the  parts  of  the  embryo.  Are  any  parts  of  the  embryo 
green  while  still  enclosed  within  the  acorn?) 

Field  observations  on  the  oaks. — Compare  the  time  of  appearance  of  the 
flowers  and  leaves  of  the  oak.  What  about  the  abundance  of  the  pollen  ? 
How  are  the  oaks  pollinated  ?  The  ament-bearing  plants  are  usually  wind- 
pollinated,  and  for  this  reason  there  is  an  abundance  of  pollen,  and  always 
in  the  form  of  dust.  Is  there  an  exception  to  this  general  rule?  How 
long  after  the  flowers  are  formed  before  the  acorn  is  ripe? 

If  there  is  time  during  excursions,  note  other  ament-bearing  plants. 

Material. — Mature  leaves,  leafy  shoots,  sprays  of  the  flowers,  both  pis- 
tillate and  staminate;  fruit  (the  acorn  in  the  cups). 


CHAPTER  LXII. 

DICOTYLEDONS   CONTINUED. 

Topic  VI :    Dicotyledons  with  distinct  petals  and 
hypogynous  flowers. 

ORDER   URTICALES. 

1162.  Lesson  VIH  The  elm  family  (Ulmaceae).— The  elm 
tree  belongs  to  this  family.  The  leaves  of  our  American  elm 
(Ulmus  americana)  are  ovate,  pointed,  deeply  serrate,  and  with 


Fig.  558. 

Spray  o£  leaves  and  flowers  of  the  American  elm ;   at  the  left  above  is  section  of 
flower   next  is  winged  seed  (a  samara). 

an  oblique  base  as  shown  in  fig.  558.  The  narrow  stipules 
which  are  present  when  the  leaves  first  come  from  the  bud  soon 
fall  away.  The  flowers  are  in  lateral  clusters,  which  arise  from 

672 


DICOTYLEDONS:    RANALES.  673 

the  axils  of  the  leaves,  and  appear  in  the  spring  before  the  leaves. 
They  hang  by  long  pedicels,  and  the  petals  are  absent.  The 
calyx  is  bell-shaped,  and  4~9-cleft  on  the  margin.  The  stamens 
vary  also  in  number  in  about  the  same  proportion.  A  section  of 
the  flower  in  fig.  558  shows  the  arrangement  of  the  parts,  the 
ovary  in  the  center.  The  ovary  has  either  one  or  two  locules,  and 
two  styles.  The  mature  fruit  has  one  locule,  and  is  margined 
with  two  winged  expansions  as  shown  in  the  figure.  This  kind 
of  a  seed  is  a  samara. 

SUGGESTIONS  FOR  STUDY  OF  THE  ELM. 

1163.  The  elm  (TJlmus  americana). 

Leaves. — What  is  the  arrangement  of  the  leaves  on  the  shoot?  Sketch 
a  leaf  showing  its  attachment  to  the  shoot,  and  the  relation  of  the  stipules; 
note  how  easily  the  stipules  fall  away. 

The  inflorescence. — Describe  the  inflorescence;  a  single  flower;  sketch 
a  single  flower  in  the  position  in  which  it  stands  on  the  tree.  Cut  away 
the  floral  envelope  on  one  side;  determine  the  number  of  stamens;  the 
number  of  pistils;  are  the  pistils  single  or  compound?  Of  how  many 
carpels  is  it  composed  ?  Sketch  a  flower  with  the  front  part  of  the  envelope 
and  the  front  stamens  removed.  What  part  of  the  floral  envelope  is  pres- 
ent? What  is  its  character  and  form?  What  are  the  relations  of  the 
sets  of  the  flower  to  each  other  ?  In  time  of  appearance  how  do  the  flowers 
compare  with  the  leaves? 

Describe  the  mature  fruit;  how  many  seed  are  present?  What  parts 
of  the  flower  are  united  in  the  fruit  ?  What  is  the  fruit  called  ? 

Material. — Spray  of  leaves  and  flowers;  it  may  be  necessary  to  collect 
them  at  different  times.  Leafy  shoots  should  be  collected  while  some  of 
the  leaves  are  still  young  in  order  to  preserve  some  with  the  stipules,  and 
they  may  be  preserved  dry  and  pressed.  Fruits  collected  at  the  time  of 
maturity  may  be  preserved  dry. 

ORDER   RANALES. 

1164.  Lesson  IX.   The  crowfoot  family  (Ranunculaceae). — 

The  marsh-marigold  (Caltha  palustris)  is  a  member  of  this  family. 
The  leaves  are  heart-shaped  or  kidney-shaped,  and  the  edge  is 
crenate.  The  bright  golden-yellow  flowers  have  a  single  whorl 
of  petal-like  envelopes,  and  according  to  custom  in  such  cases 
they  are  called  sepals.  The  number  is  not  definite,  varying  from 


6/4 


FAMILIES  OF  ANGIOSPERMS. 


five  to  nine  usually.     The  stamens  are  more  numerous,  as  is  the 

general  rule   in  the   members   of 
the    family,   but    the   number   of 
the  pistils  is  small.     Each  one  is 
separate,  and  forms  a  little  pod 
when  the  seed  is  ripe.    The  marsh- 
marigold,  as  its 
name  implies,  oc- 
curs in  marshy  or 
wet   places    and 
along  the  muddy 
banks  of  streams. 
It  is  one  of  the 
common  flowers   in   April    and 
May. 

Many  of  the  crowfoots  or  but- 
tercups (Ranunculus)  with  bright 
yellow  flowers   grow   in  similar 
situations.     The   "wood  anem- 
one"  (Anemone),    small  plants 
Diagram  of  marsh-marigold  with  white  flowers,  and  the  rue-anemone 
flower-  (Anemonella),   which   resembles  it,   both 

flower  in  woods  in  early  spring.  The  common  virgin' s-bower 
(Clematis  virginiana)  occurs  along  streams  or  on  hillsides,  climb- 
ing over  shrubs  or  fences.  The  vine 
is  somewhat  woody.  The  leaves  are 
opposite,  petioled,  and  are  composed 
of  three  leaflets,  which  are  ovate, 
three-lobed,  and  usually  strongly  „ 
toothed,  and  somewhat  heart-shaped 
at  the  base.  The  flower-clusters  are 
borne  in  the  axils  of  the  leaves,  and 
therefore  may  also  be  opposite.  The 
clusters  are  much  branched,  forming 
a  convex  mass  of  beautiful  whitish 
flowers.  The  sepals  are  colored  and  the  petals  may  be  absent, 


Fig.  559- 

Caltha  palustris,   marsh- 
marigold. 


Fig.  561- 
Diagram  of  aquilegia  flower.    (Vines.) 


DICOTYLEDONS:   KANALES. 


675 


or  are  very  small.  The  stamens  are  numerous,  as  in  the  mem- 
bers of  the  crowfoot  family.  The  pistils  are  also  numerous,  and 
the  achenes  in  fruit  are  tipped  with  the 
long  plumose  style,  which  aids  them  in 
floating  in  the  air. 

Some  of   the  characters  of   the  Ranun- 
culaceae  we  recognize  to  be  the  following: 


Fig.  562. 

Clematis  virginiana;  below  at  right  are 
pistillate  and  staminate  flowers. 


Fig.  563- 
Isopyrum  biternatum. 


The  plants  are  mostly  herbs,  the  petals  are  separate,  and  when 
the  corolla  is  absent  the  sepals  are  colored  like  a  corolla.  The 
stamens  are  numerous,  and  the  pistils  are  either  numerous  cr 
few,  but  they  are  always  separate  from  each  other,  that  is,  they 
are  not  fused  into  a  single'pistil  (though  sometimes  there  is  but 
one  pistil).  All  the  parts  of  the  flower  are  separate  from  each 
other,  and  make  up  successive  whorls,  the  pistils  terminating 
the  series.  When  the  seeds  are  ripe  the  fruit  is  formed,  and 
may  be  in  the  form  of  a  pod,  or  achene,  or  in  the  form  of  a  berry, 
as  in  the  baneberry  (Actaea). 


676  FAMILIES   OF  ANGIOSPERMS. 

SUGGESTIONS  FOR  STUDY  OF  THE  BUTTERCUP. 

1165.  The  buttercup. — If  preferred,  a  species  of  buttercup  may  be 
studied  instead  of  the  marsh-marigold,  but  a  comparison  with  the  latter 
is  desirable. 

The  entire  plant. — Describe  form  and  habit  of  the  plant;  the  character 
of  the  stem;  branching;  the  form  and  arrangement  of  the  leaves;  the 
character  of  the  roots  (these  characters  will  depend  on  the  species). 

The  inflorescence. — What  kind  of  inflorescence?  What  parts  of  the 
flower  are  present?  Describe  the  color  and  form  of  members  of  the  dif- 
ferent sets  of  the  flower.  Determine  the  number  of  members  in  each  set 
(approximately  if  not  accurately). 

Sketch  a  sepal,  a  petal  (is  a  nectar-gland  present?),  a  stamen,  and  a 
pistil,  noting  carefully  the  characters  of  each. 

Do  the  stamens  all  ripen  their  pollen  at  the  same  time?  Is  there  any 
advantage  as  regards  the  time  of  ripening  of  the  stamens  ? 

What  is  the  relation  of  the  members  of  a  set  among  themselves?  What 
is  the  relation  of  the  sets  to  each  other? 

Is  the  flower  perfect  or  imperfect,  complete  or  incomplete  ?  Is  it  regular 
or  irregular;  hypogynous,  perigynous,  or  epigynous?  Are  the  parts  of  the 
flower  free  and  distinct,  or  adherent,  or  coherent? 

If  fruit  is  present,  determine  the  number  of  seed  in  a  ripe  fruit,  and 
also  what  parts  of  the  flower  make  up  the  fruit. 

If  there  is  time,  a  comparison  of  the  flowers,  fruit,  and  leaves  of  different 
species  of  the  Ranunculus  will  be  found  interesting,  especially  species  from 
dry  and  wet  ground,  as  well  as  some  of  the  species  which  grow  in  the  water. 

Construct  the  formula  for  the  buttercup  flower;  also  construct  the  floral 
diagram. 

Material. — Entire  plants,  some  flowering  stems  with  flowers,  some  with 
fruit.  Fresh  material  when  possible. 

ORDER    PAPAVERALES. 

1166.  Lesson  X.    The  mustard  family    (Cruciferse).— This 
is  well  represented  by  the  tooth  wort  (Dentaria),  which  we  studied 
in  a  former  chapter.     The  flowers  are  regular,  and  the  parts  are 
usually  in  twos  (dimerous)  or  in  fours   (tetramerous).     (If  the 
toothwort  has  been  studied,  the  shepherd' s-purse  may  be  omitted.) 

SUGGESTIONS  FOR  STUDY  OF  THE  SHEPHERD' S-PURSE. 

1167.  The  shepherd's-purse  (Capsella   bursa-pastoris).— -If  it  is  desired 
to  study  a  species  besides  the  toothwort,  the  shepherd's-purse  will  answer. 
It  is  a  common  and  widely  distributed  species,  found  in  waste  places  and 
in  fields. 


DICOTYLEDONS:    GERANIALES.  677 

The  entire  plant. — Note  and  describe  the  habit  and  character  of  the 
plant,  i.e.,  the  size,  character  of  branching,  character  of  the  root,  position 
and  arrangement  of  the  leaves.  Compare  the  ''radicle"  (lower)  leaves 
with  the  "cauline"  (stem)  leaves  as  to  form  and  insertion.  The  radicle 
leaves  are  more  or  less  deeply  lobed  or  pinnatifid  (pinnately  cut),  while 
the  stem  leaves  are  slender,  lanceolate,  toothed,  and  often  auricled  (with 
little  ears)  at  the  base. 

The  inflorescence. — What  is  the  kind  of  inflorescence?  Determine  the 
parts  of  the  flower  present,  as  well  as  the  number  and  arrangement  of  the 
members  of  the  flower.  What  figure  which  suggests  the  name  of  the  fam- 
ily to  which  the  shepherd's-purse  and  the  tooth- 
wort  belong,  do  the  petals  make  in  the  flower  ? 

The  fruit. — What  parts  of  the  flower  are  united 
in  the  fruit  ?  Compare  the  plant  with  the  tooth- 
wort. 

Construct  the  floral  diagram  of  the  toothwort 
or  shepherd's-purse,  or  of  other  cruciferous  plant 
studied. 

Material. — Entire  plants  with 
flowers  and  fruit.  The  plant 
occurs  from  early  spring  to  au- 
tumn, and  can  be  usually  obtained 
in  a  fresh  condition  when  wanted. 

ORDER   GERANIALES. 

1168.  Lesson  XL  The 
geranium  family  (Gerani- 

acese).— The  wild  cranesbili 
has  a  perennial  underground 
rootstock.  From  this  in  the 
spring  arises  the  branched, 
hairy  stem.  The  leaves  are 
deeply  parted  into  about  five 
wedge-shaped  lobes,  which 
are  again  cut.  The  peduncles 
bear  several  purple  flowers(fig. 

564).       The  floral  formula  is       Branch  of  craJsbUM geranium    macula- 
as  follows:    Ca5,Co5,AlO,G5.   tim).showinguPPer  leaves,  flowers,  and  pods. 

The  wood-sorrel  (Oxalis),  the  balsam  or  jewelweed  (Impatiens), 
sometimes  called  "  touch-me-not,"  are  members  of  the  same  family. 


CHAPTER  LXIII. 

DICOTYLEDONS    CONTINUED. 

Topic  VII:  Dicotyledons  with  distinct  petals  and 

perigynous  or  epigynous  flowers. 

Many  trees  and  shrubs. 

ORDER   ROSALES. 

1169.  Lesson  XII.' — The  rose-like  flowers  are  an  interesting 
and  important  group.'    In  all  the  members  the  receptacle  (the 

end  of  the  stem  which 
bears  the  parts  of  the 
flower)  is  an  important 
part  of  the  flower.  It  is 
most  often  widened,  and 
either  cup-shaped  or  urn- 
shaped,  or  the  center  is 

p.^56s  elevated.        The  carpels 

Perigynous    flower    of  spiraea    (S.   lanceoiata).  are  borne  in  the  center  in 

(From  Warming.) 

the  depression,  or  on  the 

elevated  central  part  where  the  receptacle  takes  on  this  form. 
The  calyx,  corolla,  and  the  stamens  are  usually  borne  on  the 
margin  of  the  widened  receptacle,  and  where  this  is  on  the  margin 
of  a  cup-shaped  or  urn-shaped  receptacle  they  are  said  to  be 
perigynous,  that  is,  around  the  gyncecium.  The  calyx  and  corolla 
are  usually  in  fives.  There  are  three  families,  as  follows. 

678 


DICOTYLEDONS:   RO SALES. 


679 


1170.  The  rose  family  (Rosacese) .— In  this  family  there  are 
five  types,  represented  by  the 
following  plants  and  illustra- 
tions: i st.  In  spiraea  (fig.  565) 
the  receptacle  is  cup-shaped. 
There  are  five  carpels,  united 
at  the  base,  but  free  at  the  ends. 

2d.    In     the     Strawberry     the     re-    Flower  of  Fragaria  vesca  with  columnar 

ceptacle  is  conic  and  bears  the 

carpels  (fig.  566).  The  conic  receptacle  becomes  the  fleshy 
fruit,  with  the  seeds  in  little  pits  over  the  surface.  3d.  The  rasp- 
berries, blackberries,  etc., 
represented  here  by  the 
flowering  raspberry  (Rubus 
odoratus),  fig.  567.  4th. 
This  is  represented  by  the 
roses.  The  receptacle  is 
urn-shaped  and  constricted 


Fig.  567. 
Flowering  raspberry  (Rubus  odoratus). 


Fig.  568. 

Perigynous  flower  of  Rosa, 
with  contracted  receptacle. 
(From  Warming.) 


toward  the  upper  portion,  with  the  carpels  enclosed  in  the  base 
(fig.  568).  5th.  Here  the  receptacle  is  cup-shaped  or  bell-shaped 
and  nearly  closed  at  the  mouth  as  in  the  agrimony. 


68O  FAMILIES,  OF  ANGIOSPERMS. 


SUGGESTIONS  FOR  STUDY  OF  THE  STRAWBERRY. 

1171.  The  strawberry  (Fragaria  vesca). 

Describe  the  appearance  of  the  entire  plant.  What  different  stems  are 
there  ?  What  purpose  does  each  kind  of  stem  serve  ?  Sketch  and  describe 
a  leaf. 

The  inflorescence. — What  is  the  kind  of  inflorescence  ? 

The  flower. — Determine  the  parts  of  the  flower  present.  Describe  each 
set  of  members  of  the  flower,  naming  the  kind  of  calyx  and  corolla.  Are 
the  sets  of  members  free?  Are  the  members  of  each  set  distinct?  To 
take  the  flower  as  a  whole  in  its  young  condition  (just  opening),  what  is 
the  relation  as  regards  position  and  elevation  of  the  different  sets  to  each 
other?  Is  the  flower  perigynous  or  hypogynous? 

What  is  the  end  of  the  stem  called  to  which  the  parts  of  the  flower  are 
attached  ? 

Do  all  the  flowers  of  the  strawberry  form  fruit?  When  you  have  deter- 
mined this,  determine  the  reason  if  you  can. 

The  fruit. — What  parts  of  the  flower  are  united  to  form  the  fruit?  What 
is  such  a  fruit  called  ?  What  part  of  the  flower  forms  the  fleshy  part  of  the 
fruit?  What  parts  of  the  flower  are  united  in  the  seed?  What  is  such  a 
seed  called? 

How  does  seed  distribution  come  about  in  such  plants  as  the  strawberry  ? 
How  are  strawberry  plants  usually  propagated? 

Material. — Entire  plants  with  runners;    flowers;    fruit. 

1172.  Lesson  XIII.    Plums,  cherries,   pears,  apples.      The 
almond  or  plum  family  (Drupaceae).— The  members  of  this 
family   are  trees   or  shrubs.     The   common   choke-cherry   (fig. 
569)  will  serve  to  represent  one  of  the  types.     The  flowers  of 
this  species  are  borne  in  racemes.     The  receptacle  is  cup-shaped. 
Only  one  seed  in  the  single   carpel   (sometimes  two   carpels) 
matures  as  the  calyx  falls  away.     The  outer  portions  of  the 
ovary  become  the  fleshy  fruit,  while  the  inner  portion  becomes 
the  hard  stone  with  the  seed  in  the  center.     Such  a  fruit  is  a 
drupe. 

The  floral  formula  for  this  family  is  as  follows: 

Ca5,Co5,Ai5-2o  or  30,01. 

The  apple  family   (Pomacese).— This  family  is  represented 
by   the   apples,    pears,    quinces,  June-berries,    hawthorns,    etc. 


DICOTYLEDONS:    RO SALES.  68 1 

The  members  are  trees  or  shrubs.  The  receptacle  is  some- 
what cup-shaped  and  hollow.  The  perianth  and  stamens  are  at 
first  perigynous,  but  become  epigynous  (upon  the  gyncecium) 
by  the  fusion  of  the  receptacle  with  the  carpels.  The  floral 


Fig.  569. 

Choke-cherry  (Prunus  virginiana).  Leaves, 
flower-raceme,  and  section  of  flower  at  right. 

formula  is  thus  Ca5,Co5,Aio-5-5  or  10-10-5,01-5.  The  carpels 
are  united,  but  the  styles  are  free.  In  fruit  the  united  carpels 
fuse  more  or  less  with  the  receptacle. 

SUGGESTIONS  FOR  STUDY  OF  THE  APPLE. 

1173.  The  apple  (Pyrus  malus). 

Leaves. — Determine  the  arrangement  of  the  leaves  on  the  shoot;   sketch 
a  leaf. 

The  inflorescence. — Determine  the  kind  of  inflorescence. 

The   flower. — Study  several   flowers   to  compare   the   variation  in   the 


682 


FAMILIES   OF  ANGIOSPERM^, 


number  of  the  parts  or  members  of  the  flower.     What  parts  of  the  flower 
are  present? 

Make  a  long  section  of  the  flower  and  sketch  showing  the  parts  and 
their  relation  to  each  othe- 


Fig.  570- 
Flower  of  pear.     (After  Warming.) 

Determine  the  number  of  members  in  each  set;  the  relation  of  the  mem- 
bers of  a  set  to  each  other;  the  relation  of  the  sets  among  themselves. 
Give  the  names  which  are  applied  to  these  relations. 

The  fruit. — What  parts  of  the  flower  are  united  in  the  fruit?  Make 
longitudinal  and  cross  sections  of  an  apple,  name  the  parts  and  show 
from  which  part  of  the  flower  each  part  of  the  fruit  comes.  What  is  the 
fruit  of  an  apple-tree  called? 

Material. — Spray  of  leaves  and  flowers;    mature  fruit. 

1174.  Lesson  XIV.  The  pea  family  (Papilionacese).—  This 
family  is  well  represented  by  the  common  pea.  The  flower  is 


Fig.  571- 

Details  of  pea  flower;  section  of  flower,  perianth  removed  to  show  the  diadelphous 
stamens,  one  single  one,  and  nine  in  the  other  group.     (From  Warming.) 

butterfly-like  or  papilionaceous,  and  the  showy  part  is  made  up 
of  the  five  petals.     The  petals  have  received  distinct   names 


DICO  T  YLED ONS  :   RO  SALES. 


683 


here  because  of  the  position  and  form  in  the  flower.     At  fig. 

572    the   petals  are   separated   and  shown 

in   their   corresponding   positions,  and   the 

names    are    there    given.       The  flower   is 

irregular  and  the  parts  are  in  fives,  except 

the  carpel,  which   is  single.     The  calyx  is 

gamosepalous  (coherent),  the  corolla   poly- 

petalous  (distinct).    The  ten  stamens  are  in 

two  groups,  one  separate  stamen  and  nine 

united;    they  are   thus    diadelphous    (two 

brotherhoods).     The  fruit  forms  a  pod  or  Fis-  572. 

,  ..          ,  Corolla  of  pea.   *S,stand- 

legume,  and  at  maturity  splits  along  both  ard;   w,  wings-,  K,  two 

petals  forming  keel. 

edges. 

There  are  three  families  in  the  legume-bearing  plants:  ist, 
including  the  locusts,  cassias,  etc. ;  2d,  the  pea  family,  including 
peas,  beans,  clovers,  ground-nuts,  or  peanuts,  vetches,  des- 
modium,  etc.;  3d,  including  the  sensitive  plants  like  mimosa. 

SUGGESTIONS  FOR  STUDY  OF  THE  PEA. 

1175.  The  pea  (Pisum  sativum). 

The  entire  plant. — Describe  the  entire  plant,  the  branching,  the  means 
for  support  (compare  different  cultivated  varieties  in  respect  to  size,  habit, 
and  means  for  support  if  practicable). 

The  leaf. — Sketch  a  leaf;  name  the  different  parts;  what  kind  of  a 
leaf  is  it?  Does  the  leaf  serve  any  purpose  for  the  mechanical  support  of 
the  plant?  How? 

The  inflorescence.— What  is  the  kind  of  inflorescence  ? 

The  flower. — Is  it  regular  or  irregular  ? 

The  calyx. — Describe  the  calyx.  How  many  sepals  are  indicated  ?  Are 
the  sepals  distinct  or  coherent?  What  name  is  applied  to  this  kind  of 
a  calyx? 

The  corolla.— What  are  the  relations  of  the  petals  to  each  other?  What 
term  is  applied  to  indicate  this  relation?  Sketch  a  flower,  and  name  the 
different  parts  of  the  corolla;  what  name  is  given  to  such  a  flower? 

The  stamens  (remove  the  corolla). — How  many  stamens  are  there?  What 
is  their  relation  to  each  other?  What  terms  are  used  to  indicate  such  a 
relation  of  stamens  of  each  other? 

The  pistil. — How  many  carpels  in  the  pistil  ?  Is  it  simple  or  compound  ? 
Sketch  a  young  pistil,  naming  the  parts. 


684  FAMILIES  OF  ANGIOSPERMS. 

The  fruit. — What  parts  of  the  flower  are  united  in  the  fruit?  Describe 
the  fruit.  What  is  such  a  fruit  called  ?  How  are  the  seeds  freed  ?  What 
is  the  difference  between  a  fruit  and  a  seed  in  the  pea  plant? 

The  clover  (Trifolium). — If  it  is  desired  to  study  a  clover,  study  one 
in  a  similar  way. 

Nitrogen  gatherers. — The  pea,  clovers,  etc.,  are  sometimes  called  nitro- 
gen gatherers  (see  Chapter  IX).  During  an  excursion  let  the  pupils  dig  up 
different  leguminous  plants,  like  the  pea,  clover,  lupine,  etc.,  and  search 


Fig.  573. 
Spray  of  leaves  and  flowers  of  the  sugar-maple. 

for  the  "tubercles"  on  their  roots,  comparing  the  form  of  the  tubercles 
on  the  different  kinds  of  plants. 

Pollination. — If  the  flowers  of  Cytisus  from  a  conservatory  are  at  hand, 
attempt  to  press  the  point  of  a  pencil  in  between  the  parts  of  the  keel  in 
the  case  of  flowers  where  these  parts  are  still  closed;  describe  the  action 
of  the  stamens  in  throwing  the  pollen.  How  could  cross-pollination  be 
brought  about  in  such  a  flower  by  the  visits  of  insects? 

Study  the  common  lupine  (Lupinus  perennis)  in  the  same  way.  Study 
the  pea  flower  with  the  same  object  in  view;  has  the  pea  flower  become 
adapted  to  self-pollination? 

Material. — Sprays  of  leaves  and  flowers;  fruit.  Material  can  usually 
be  obtained  fresh  early  in  the  spring  and  for  some  time  later. 


D  ICO  T  YLED  ONS  :   SA  FIND  A  LES. 


685 


Fig.  574- 


ORDER   SAPINDALES. 

1176.  Lesson  XV.  The  maple  family  (Aceraceae). — Fig.  573 
represents  a  spray  of  the  leaves  and  flowers  of  the  sugar-maple 
(Acer  saccharinum),  a  large  and  handsome  tree.  The  leaves 
are  opposite,  somewhat  ovate  and  heart-shaped,  with  three  to 
five  lobes,  which  are  again  notched.  The  clusters  of  flowers 
are  pendulous  on  long  hairy  pedicels.  The  petals  are  wanting. 
The  calyx  is  bell-shaped 
and  several  times  lobed, 
usually  five  times.  The 
stamens  are  variable  in 
number.  The  ovary  is 
two-lobed  and  the  style 
deeply  forked.  The  fruit 
forms  two  seeds,  each  with 

n      Inno1     wincr-likp      Pxnan-       Seeds  and  flowers  of  sugar-maple.    Attherightis 
1     a  pistillate  flower,  in  the  middle  a  staminate  flower, 

sion  as  shown  in  the  figure.  and  at  the  left  the  two  seeds  formins  *  samara. 
The  flowers  of  the  maple  are  polygamo-dicecious,  that,  is  the 
male    members    (stamens)  and   female  members  (carpels)  may 
be  in  the  same  flower  or  in  different  flowers. 

SUGGESTIONS  FOR  STUDY  OF  THE  SUGAR-MAPLE. 

1177.  The  sugar-maple  (Acer  saccharinum).  —  (Another  species  may 
be  studied  if  desired.) 

Leaves. — Determine  the  form  and  arrangement  of  the  leaves;  sketch  a 
leaf. 

Inflorescence. — Describe  the  character  of  the  inflorescence;  sketch  a 
flower  cluster. 

Flowers. — Select  several  different  flowers,  some  from  different  trees, 
and  compare  them  carefully  to  see  if  the  members  of  the  flower  are  the 
same  in  all.  Sketch  several  to  show  the  general  character. 

What  parts  of  the  flower  are  present?  Describe  the  form  and  character 
of  each  set  of  members,  and  their  relation  to  each  other.  Determine  the 
number  of  members  in  each  set  and  their  relations  among  themselves. 
Study  several  flowers  to  make  this  out. 

The  fruit. — Sketch  a  fruit.  What  parts  of  the  flower  are  united  in  the 
fruit? 

If  there  is  time,  it  will  be  found  instructive  to  compare  the  flowers  of 
another  species  of  maple,  like  the  red  maple,  with  the  sugar-maple.  Ex- 


686  FAMILIES   OF  ANGIOSPERMS. 

amine  different  flowers  from  several  different  trees  in  order  to  compare  the 
different  sizes  of  the  stamens  and  pistils  in  different  flowers,  and  the  facts 
with  reference  to  the  presence  or  absence  of  any  of  the  members  in  certain 
of  the  flowers.  Compare  the  leaves  of  the  red  maple  with  those  of  the 
sugar -maple  also. 

Material. — Leafy  shoots,  either  fresh  or  pressed  and  dried.  Flowers; 
fresh  as  they  appear  in  the  spring;  if  they  cannot  be  studied  immediately, 
they  may  be  preserved  in  alcohol  or  in  formalin.  They  are  better  fresh. 

Fruits,  collected  when  mature  preserved  dry. 

Omit  the  study  of  the  horse-chestnut  unless  it  is  desired  to 
study  it  instead  of  the  maple,  since  it  belongs  to  the  same  order. 

1178.  The  buckeye  family  (Hippocastanacese).— The  horse- 
chestnut  (^sculus  hippocastanum)  is  largely  planted  in  the 
Northeastern  United  States  as  an  ornamental  tree.  It  is  also 
self -seeding  in  waste  places.  The  family  is  represented  in 
other  places  by  other  species,  the  buckeye,  for  example,  from 
which  the  family  gets  its  common  name,  occurs  in  Ohio  (the 
Buckeye  State). 

SUGGESTIONS  FOR  STUDY  OF  THE  HORSE-CHESTNUT. 

The  horse-chestnut  (JEsculus  hippocastanum;. 

The  leaves. — Note  the  form  and  arrangement  of  the  leaves.  Sketch  a 
leaf  to  show  its  form  and  the  parts.  What  kind  of  a  leaf  is  it? 

The  inflorescence  (mixed  racemose). — The  flowers.  What  parts  of  the 
flower  are  present?  Is  the  flower  complete  or  incomplete;  regular  or  irreg- 
ular; perfect  or  imperfect? 

Describe  the  calyx;  the  corolla;  describe  a  petal,  its  form  and  color. 
How  many  petals  present? 

The  stamen. — How  many  present  ?     Sketch  a  stamen. 

The  pistil. — Describe  the  form  of  the  pistil,  its  parts;  how  many  carpels 
are  represented  in  the  pistil?  What  is  the  character  of  the  surface  of  the 
ovary? 

The  mature  fruit. — What  is  the  character  of  the  surface  of  the  mature 
fruit?  Describe  the  form  of  the  fruit.  What  parts  of  the  flower  are  united 
to  form  the  fruit?  What  is  the  difference  between  the  fruit  and  a  seed  in 
the  horse-chestnut?  Examine  the  embryo  in  the  seed;  note  its  large 
cotyledons  and  the  well-developed  hypocotyl.  Why  is  the  embryo  not  good 
for  food  for  man? 

Construct  the  floral  diagram  of  the  horse-chestnut  flower. 

Material. — Sprays  of  leaves  and  flowers,  collected  fresh.     Mature  fruits. 


CHAPTER  LXIV. 

DICOTYLEDONS   CONTINUED. 

Topic  VIII:  Dicotyledons  with  distinct  petals,  hypo- 
genous  and  irregular  flowers. 

OKDER  PARIETALES. 

1179.  Lesson  XVI.  The  violet  family  (Violacese).— This 
family  is  represented  by  the  common  blue  violet,  the  yellow 
violet,  the  pansies,  heartsease,  sweet  violet,  etc. 

SUGGESTIONS  FOR  STUDY  OF  THE  BLUE  VIOLET. 

The  blue  violet  (Viola  cucullata). 

The  entire  plant. — Describe  the  character  and  habit  of  the  plant,  the 
short  underground  stem,  the  "radicle"  leaves,  the  erect  flower-scapes 
which  bear  the  conspicuous  blue  flowers,  and  the  short,  curved  stems 
beneath  the  soil  or  debris  which  bear  the  closed  inconspicuous  flowers. 
Sketch  a  leaf,  showing  the  form  and  venation.  What  is  the  form  of  the 
leaf  and  the  character  of  the  margin? 

The  blue  flowers. — Sketch  a  flower.  Is  the  flower  regular  or  irregular; 
complete  or  incomplete;  perfect  or  imperfect? 

The  calyx. — Describe  the  form  of  the  calyx;  how  many  sepals  are  indi- 
cated ? 

The  corolla. — How  many  petals  are  present?  Remove  them  and  note 
carefully  the  form  of  each  one  and  the  position  in  the  flower.  In  the 
"spurred"  one  look  for  nectar-glands. 

The  stamens. — Determine  the  number  of  the  stamens.  Are  they  united 
together  by  their  anthers  ?  If  so,  the  stamens  are  said  to  be  syngenecious. 
Are  the  stamens  of  different  sizes  ?  Describe  the  form  of  the  different  ones 
and  the  relation  of  certam  peculiar  ones  to  the  spur  of  the  corolla. 

687 


688 


FAMILIES   OF  ANGIOSPERMS. 


The  pistil. — Describe  the  form  of  the  pistil  and  the  relation  of  the  stamens 
and  pistils. 

The  closed  (cleistogamous)  flowers. — These  are  on  shorter,  curved, 
scapes  which  hold  them  beneath  the  soil  or  debris.  Compare  them  with 
the  blue  flowers.  What  parts  of  the  flower  are  absent? 

The  fruit. — Make  a  cross-section  of  the  fruit  and  determine  how  many 


Fig.  575- 

Viola  cucullata ;  blue  flowers  above,  cleistogamous  flowers  smaller  and  curved  below. 
Section  of  pistil  at  right. 

carpels  are  represented  in  the  pistil.     Note  the  numerous  seeds  and  their 
attachment. 

Pollination  of  ^violets. — If  a  sweet -violet  flower  or  the  flowers  of  the 
pansy  are  convenient,  study  the  stamens  and  pistil  of  the  open  flowers. 
Remove  the^qorolla,  and  note  the  position  of  the  anthers  with  reference  to 
the  pistil.  Note  the  peculiar  enlarged  stigma  with  an  opening  in  front, 


DICOTYLEDONS:   MYRTALES. 


689 


and  the  lip  below.  Move  a  pencil  into  a  flower,  endeavoring  to  imitate  the 
entrance  of  an  insect,  and  try  to  determine  how  cross-pollination  takes 
place.  Compare  the  blue  flowers  of  the  blue  violet. 

The  small  closed  flowers  are  called  cleistogamous,  and  they  are  self- 
pollinated,  because  being  closed,  and  because  of  the  position  of  the  anthers 
around  the  stigma,  the  pollen  from  the  opening  anthers  comes  directly  in 
contact  with  the  stigma.  In  the  flowers  of  the  pansy  cross-pollination 
often  takes  place  through  the  agency 
of  insects.  While  the  blue  flowers 
of  the  blue  violet  rarely  set  fruit, 
nevertheless  pollination  and  fertili- 
zation do  take  place  in  some  of  the 
flowers,  though  fruit  sets  more  abun- 
dantly in  the  cleistogamous  flowers. 

Material. — Entire  plants  with  the 
flowers;  collect  some  early  in  the  sea- 
son when  the  blue  flowers  are  abun- 
dant, and  some  later  when  the  small 
flowers  underneath  the  soil  or  leaves 
are  formed.  Mature  fruit  is  also 
desirable. 

Topic  IX:  Dicotyledons 
with  distinct  petals  and 
epigynous  flowers. 

ORDER   MYRTALES. 

1180.  Lesson  XVII.  The  even- 
ing-primrose family  (Onagra- 

cese). — In  the  evening  primrose 
(oenothera)  the  flowers  are  ar- 
ranged in  a  loose  spike  along 
the  end  of  the  stem,  each  one 
situated  in  the  axil  of  a  leaf- 
like  bract.  The  flowers  of  the 
family  are  very  characteristic,  as  shown  here.  They  are  sessile 
in  the  axil  of  the  bract,  and  the  calyx  forms  a  long  tube  by  the 
union  of  the  sepals,  only  the  end  of  the  tube  being  divided  into 
the  individual  parts,  showing  four  lobes.  On  the  edge  of  the 
open  end  of  the  calyx-tube  are  seated  the  four,  somewhat  heart- 


Fig.  576. 

Section  of  flower 
of  CEnothera. 


6go 


FAMILIES   OF  ANGIOSPEKMS. 


Fig.  577- 

Evening  primrose  (CEnothera  biennis),  showing  flower-buds,  flowers,  and  seed- 
pods.     (From  Kerner  and  Oliver.) 


DICO  T  YLED  ONS  :   M  YR  TA  LES. 


691 


shaped,  yellowish  petals,  and  here  are  also  seated  the  eight 
stamens.  The  four  carpels  are  united  into  a  single  pistil  within 
the  base  of  the  calyx-tube  and  united  with  it,  so  that  the  calyx- 
tube  seems  to  be  on  the  end  of  the  pistil.  The  flowers  soon  fade 
and  fall  away  from  the  pistil,  and  this  grows  into  an  elongated 


Fig.  578. 
Wild  carrot. 

four-angled  pod.  Since  the  lower  flowers  on  the  stem  are  the 
older,  we  find  nearly  mature  fruit  and  fresh  flowers,  with  all 
intermediate  grades,  on  the  same  plant. 

The  plants  grow  by  roadsides  and  in  old  fields.     They  are 
from  locm  to  a  meter  or  more  high  (one  to  five  feet).       The 


692 


FAMILIES   OF  ANGIOSPERMS. 


leaves  are  lanceolate  or  oblong,  toothed  and  repand  on  the  margin. 
In  many  of  the  species  of  the  family  the  parts  of  the  flower  are 
in  fours  as  in  the  evening  primrose,  but  in  others  the  number  is 
variable. 

ORDER   UMBELLALES. 

1181.    Lesson   XVIII.    The  parsley  family   (Umbelliferae).  — The   wild 
carrot  (Daucus  carota)  is  common  in  old  fields  during  August  and  Septem- 


Fig.  579- 
Single  umbel  of  the  wild  carrot. 

her.     The  leaves  are  deeply  divided  and  the  lobes  are  notched  (pinnately 
decompound).     The  flowers  form  umbels,   since   the  pedicels  are  all  of 


Fig.  580. 
Flower  of  wild  carrot 


Fig.  581. 
Section  of  flower. 


Fig.  582. 
Seed  of  wild  carrot. 


about  the  same  length,  and  many  of  them  radiate  from  the  same  point. 
In  the  carrot,  and  in  most  of  the  parsley  family,  the  umbel  is  a  compound 
one,  as  shown  in  the  illustration.  The  calyx  is  firmly  united  with  the 


DICOTYLEDONS:    UMBELLALES.  693 

walls  of  the  ovary,  which  is  formed  of  two  united  carpels.  The  five  white 
petals  as  well  as  the  five  stamens  arise  from  the  margin  of  the  ovary  around 
the  two  styles.  No  portion  of  the  calyx  is  free  in  the  wild  carrot,  though 
in  some  other  members  of  the  family  there  are  small  calyx  teeth.  The 
fruit  is  bristly  and  the  surface  of  the  umbel  becomes  concave  in  age.  The 
floral  formula  is  as  follows:  Ca5,Co5,A5,G2. 

The   cornel  or  dogwood   family   and   the   aralia  family   both  have   the 
flowers  in  umbels,  and  are  thus  related  to  the  parsley  family. 


CHAPTER  LXV. 


DICOTYLEDONS    CONCLUDED. 


Topic  X:   Dicotyledons  with  united  petals,  flower 
parts  in  four  whorls. 

ORDER    POLEMONIALES. 

1182.  Lesson  XIX.     The  mint  family  (Labiatse).— The  mint 
family  contains  a  large  number  of  genera  and  takes  its  common 

name  from  the  mints,  of  which 
there  are  several  species  belong- 
ing to  the  genus  Mentha.  In  the 
figure  of  the  "dead-nettle"  (La- 
mium  amplexicaule),  which  is  also 
one  of  the  members  of  this  family, 
we  see  that  the  lobes  of  the  irregular 
corolla  are  arranged  in  such  a 
manner  as  to  suggest  two  lips,  an 
upper  and  a  lower  one.  From 
this  character  of  the  corolla,  which 
obtains  in  nearly  all  the  members, 
the  family  receives  its  name  of 
Labiatce.  The  calyx  is  five-lobed. 
The  stamens,  four  in  number, 
arise  from  the  tube  of  the  corolla, 
and  converge  in  pairs.  The 
ovary  is  divided  into  four  lobes, 
maturity  of  the  seed  these  form  four  nutlets. 

694 


Fig.  583. 

Spray  of  dead-nettle  (Lamium  am- 
plexicaule), leaves  and  flowers. 

and    at    the 


DICOTYLEDONS:   POLEMONIALES.  695 

The  leaves  are    rounded,  crenate    on    the   margins,   the   lower 

ones   petioled    and    heart-shaped,    and 

the    upper    ones     sessile    and    clasping 

around    the    stem    beneath    the   flower 

clusters.     From   the   clasping   character 

of  the  upper  leaves   the    plant   derives 

its  specific  name  of  amplexicaule.     The 

plant    OCCUrs     in    Waste      places    and      is      Diagram  TfLam^m  flower. 

rather  common. 

SUGGESTIONS  FOR  STUDY  OF  A  LABIATE  FLOWER. 

1183.  The  catnip  (Nepeta  cataria). — While  the  "dead-nettle"  is  used 
here  to  illustrate  the  mint  family,  other  species  may  be  studied  instead. 
The  exercise  is  written  for  the  catnip  (Nepeta  cataria),  a  very  common 
weed  occurring  from  July  to  September.  If  fresh  material  is  not  at  hand 
when  the  study  is  made,  dried  entire  plants,  and  the  flowers,  in  formalin 
may  be  used,  unless  it  is  preferred  to  use  fresh  material  of  some  other 
available  species.  In  that  case  the  dead-nettle  here  illustrated,  and  the 
outline,  will  serve  as  a  guide  for  the  study. 

The  entire  plant. — Note  the  habit,  the  character  of  the  branching,  the 
shape  of  the  stem,  the  character  of  the  surface.  Note  the  form  and  arrange- 
ment of  the  leaves.  Is  the  plant  annual,  biennial,  or  perennial  ? 

The  inflorescence. — What  is  the  inflorescence?  The  flower:  the  parts 
present;  the  calyx,  form  and  relation  of  parts;  the  corolla,  form,  relation 
of  parts,  into  what  two  parts  is  the  corolla  divided,  the  name  of  the  two 
parts,  the  number  of  petals  in  each  part,  Note  the  stamens,  number, 
size,  position  in  the  flower.  The  pistil;  sketch  a  pistil  showing  the  nutlets, 
the  long  style. 

To  study  the  stamens  remove  a  corolla,  split  it  open  down  one  side  and 
spread  it  out  on  a  glass  slip  and  mount  in  water;  or  pin  it  to  a  cork.  Ex- 
amine with  a  good  hand  lens,  or  with  the  lower  power  of  the  microscope. 

Construct  the  floral  diagram. 

Cross-pollination  by  insects. — Study  the  adaptations  of  the  flower  for 
this  purpose.  The  lower  lip  is  the  landing  place,  and  the  upper  lip  is  the 
"banner."  If  there  are  color  markings  on  any  portion  of  the  flower  which 
serve  to  guide  the  insect  in  entering  the  flower,  describe  them  and  note  the 
location.  With  a  needle  imitate  the  entrance  of  an  insect  into  the  flower 
and  determine  the  way  in  which  cross-pollination  takes  place. 

Compare  if  possible  other  members  of  the  mint  family  in  the  study  of 
cross-polli  nation . 

Material. — Entire  plant  with  flowers  and  ripe  fruit.     If  fresh  plants  are 


696  FAMILIES   OF  ANGIOSPERMS. 

not  at  hand,  those  that  have  been  pressed  and  dried  may  be  used  for  the 
study  of  the  entire  plant  and  of  the  leaves.  The  flowers  may  be  preserved 
in  formalin. 

1184.  Lesson  XX.  The  figwort  family  (Scrophulariaceae). — The  mullein 
(Verbascum),  toad-flax  (Linaria),  turtle -head  (Chelone),  etc.,  are  members 
of  the  figwort  family.  The  plants  are  mostly  herbs.  The  stamens  are 
usually  didynamous  (four  in  two  pairs,  one  pair  shorter  than  the  other) 
or  diandrous  (two  stamens).  The  stamens  are  inserted  on  the  two-lipped 
corolla-tube,  which  is  more  or  less  irregular.  In  some  genera  there  are 
five  stamens,  as  in  Verbascum. 

SUGGESTIONS  FOR  STUDY  OF  A  FIGWORT. 

The  Toad-flax  (Linaria  vulgaris). — The  toad-flax  is  widely  distributed, 
growing  in  waste  places  as  a  weed  from  June  to  October. 

The  entire  plant. — Note  the  short,  pale  green  perennial  rootstock;  the 
longer  erect  annual  stem;  is  it  simple  or  branched?  Leaves,  form,  and 
arrangement. 

The  inflorescence. — The  kind  of  inflorescence.  The  flower. — What 
parts  of  the  flower  are  present?  Describe  the  different  parts.  The  calyx. 
— How  many  sepals  indicated?  What  is  the  form  of  the  calyx?  The 
corolla. — Form.  How  many  petals  indicated?  Describe  the  form  of 
the  corolla  and  its  parts.  The  stamens. — How  many,  their  position,  size? 
What  is  the  significance  of  the  difference  in  the  size  of  the  stamens  ?  The 
pistil. — Form,  parts;  form  of  the  ovary;  how  many  carpels  present  in 
the  pistil  ? 

Study  the  adaptation  of  the  flower  for  cross-pollination  by  the  aid  of 
insects;  the  lower  lip  of  the  corolla  as  a  landing  place;  since  insects  are 
supposed  to  be  attracted  by  bright  colors,  what  portion  of  the  flower  serves 
thus  to  direct  the  insect  ? 

Note  the  spur  on  the  corolla,  and  the  nectary  inside ;  what  kinds  of  insects 
visit  this  flower?  Imitate  with  the  end  of  a  pencil  the  entrance  of  an 
insect  in  a  flower  and  endeavor  to  make  out  how  cross-pollination  takes 
place. 

Seed  distribution. — Examine  ripe  seed-pods,  dry  some  of  them,  and 
then  take  some  of  the  dry  ones  and  place  in  water.  Describe  the  action 
of  the  pod  in  scattering  the  seeds,  and  the  causes. 

Other  members  of  the  family  are  interesting  to  compare  with  the  toad- 
flax, as  the  beard-tongue  (Penstemon  pubescens),  turtle-head  (Chelone 
glabra),  monkey-flower  (Mimulus  ringens),  etc. 

Material. — Entire  plants  with  the  underground  stems.  Flowers  and 
fruit.  If  fresh  material  cannot  be  had  at  the  time  of  the  study,  dried  plants 
(pressed)  will  answer  for  the  study  of  the  entire  plant.  Flowers  may  be 
preserved  in  formalin;  fruits  dry. 


DICO  T YLED ONS  :    CA MPANULALES. 


697 


ORDER  CAMPANULALES. 
1185.  Lesson  XXI.     The  thistle  family  ( Composite) .— In  all 

the  composites,  the  flowers  are 
grouped  (aggregated)  into 
"heads,"  as  in  the  sunflower, 
where  each  head  is  made  up  of 
a  great  many  flowers  crowded 
closely  together  on  a  widened 
receptacle.  The  family  is  a 
large  one,  and  is  divided  into 
several  sections  according  to 
the  kinds  of  flowers  and  the 
different  ways  in  which  they 
are  combined  in  the  head.  In 
the  asters  there  is  one  common 
type  illustrated  in  fig.  585  by 
the  Aster  novcz-anglice.  In  the 
aster,  as  is  well  shown  in  the 
figures,  the  head  is  composed 
of  two  kinds  of  flowers,  the 
tubular  flowers  and  the  ray 


Fig.  585- 
Aster  novae-angliae. 


'     Fig.  586. 
Head  of  flowers  of  Aster  novae-angliae. 


flowers.  In  the  tubular  flowers  the  corolla  is  united  to 
form  a  slender  tube,  which  is  five-notched  at  the  end, 
representing  the  five  petals.  In  the  ray  flowers  the  corolla 


698 


FAMILIES   OF  ANGIOSPERMS. 


is  extended  on  one  side  into  a  strap-shaped  expansion.  To- 
gether these  strap-shaped  corollas  form  the  "rays"  of  the 
head.  The  corolla  is  split  down  on  one  side,  which  permits  the 


Fig.  587-  Fig.  588. 

Ray  flower  of  Aster  no-      Tubular  flower 
vaeangliae.  of  aster. 


Fig.  589.  Fig.  590. 

Tubular         flower        Syngenecious 
opened  to  show  syn-    stamens  opened  to 
genecious  stamens.        show  style  and  two 
stigmas. 


end  then  to  expand  and  form  the  "strap."  This  is  a  ligula, 
or  more  correctly  speaking  a  false  ligula.  In  fact  the  ray  flower 
is  bilabiate.  By  counting  the  "teeth"  of  the  false  ligula  there 
are  found  only  three,  which  indicates  that  the  strap  here  is 
made  up  of  only  three  parts  of  the  5-merous  corolla.  The  two 
other  limbs  of  the  corolla  are  rudimentary,  or  suppressed,  on 
the  opposite  side  of  the  tube.  True  ligulate  flowers  are  found 
in  the  chicory,  dandelion,  or  in  the  hieracium,  where  the  five 
points  are  present  on  the  end  of  the  ligula. 

The  calyx  tube  in  the  aster,  as  in  all  of  the  composites,  is 
united  with  the  ovary,  while  the  limb  is  free.  In  the  aster,  as 
in  many  others,  the  limb  is  divided  into  slender  bristles,  the 
pappus.  (In  some  of  the  composites  the  pappus  is  in  the  form 
of  scales.)  The  stamens  are  united  by  their  anthers  into  a  tube 
(syngenecious)  which  closely  surrounds  the  style.  (In  Am- 
brosia the  anthers  are  sometimes  distinct.)  The  style  in  pushing 


com. 


DICOTYLEDONS:    CAMPANULALES.  699 

through  brushes  out  some  of  the  pollen  from  the  anthers  and 
bears  it  aloft  as  in  the  bell-flower,  but  the 
stigmatic  surface  is  not  yet  mature  and 
expanded,  so  that  close  pollination  cannot 
take  place.  There  are  usually  no  stamens 
in  the  ray  flowers.  The  ovary  is  composed 
of  two  carpels,  as  is  shown  by  the  two  styles, 
but  there  is  only  one  locule,  containing  an 
erect,  anatropous,  ovule.  posite  flower.  (Vines.) 

The  floral  formula  for  the  composite  family  then  is  as  fol- 
lows: Ca5,Co5,A5,G2.  A  number  of  the  composites  have  only 
tubular  flowers,  as  in  the  thoroughwort  (Eupatorium)  and  ever- 
lasting (Antennaria). 

SUGGESTIONS  FOR  STUDY  OF  AN  ASTER. 

1186.  The  aster  (Aster  novae-angliee).—  (Some  other  species  may  be 
selected  if  it  is  more  convenient.) 

The  entire  plant.  —  Describe  the  entire  plant;  the  character  of  the  stem; 
the  position  of  the  leaves;  their  form  on  different  portions  of  the  stem; 
their  attachment  to  the  stem.  Compare  the  "radicle"  leaves  with  the 
stem  leaves. 

The  inflorescence.  —  Describe  the  inflorescence,  and  the  position  of  the 
flower  heads. 

A  single  head  of  flowers.  —  Describe  the  involucre.  What  different 
kinds  of  flowers  are  present?  What  is  the  position  of  each  kind  in  the 
head?  Determine  the  approximate  number  of  each  kind  of  flowers  in 
a  head. 

The  ligulate  flowers.  —  Remove  one  from  the  head  and  sketch  it,  show- 
ing the  different  parts.  How  many  petals  are  indicated  in  the  strap? 
How  many  petals  are  in  the  tubular  portion  of  the  ligulate  flower?  Is 
this  a  t.ue  ligula?  Why?  Is  the  calyx  present,  and  what  represents 
it  ?  Split  open  the  corolla-tube,  and  determine  whether  or  not  the  stamens 
are  present.  Is  the  pistil  present  in  the  ligulate  flower? 

The  tubular  flowers.  —  Describe  the  corolla.  How  many  petals  are 
indicated  in  the  corolla  -tube  ?  What  is  such  a  corolla  called? 

The  stamens.  —  Split  open  the  corolla-tube  down  one  side,  and  sketch 
to  show  the  position  of  the  stamens,  and  their  relation  to  each  other.  Split 
open  the  anther  column,  spread  it  out,  and  sketch  to  show  the  relation 
of  the  stamens  to  each  other,  and  the  pistil  within. 

Material.  —  Entire  plants  in  flower;  also  some  of  the  mature  fruit  heads. 

The  goldenrod  (Solidago).  —  (As  an  alternate,  if  desired,  for  the  aster.) 


700 


FAMILIES   OF  ANGIOSPERMS. 


If  it  is  desired  to  study  the  goldenrod  instead  of  the  aster,  it  will  be  well 
to  make  a  comparison  with  the  aster,  and  the  account  of  the  aster  here 
given  will  serve  as  a  guide  for  the  study  of  the  goldenrod.  The  daisy  is 
also  a  good  one  to  compare  with  the  aster,  and  the  outline  for  the  study 
of  the  aster  here  given  will  answer  for  the  basis  of  such  a  study. 

1187.  Lesson  XXII.  The  chickory 
family  (Cichoriaceae).  —  The  rattle- 
snake-weed (Hieracium  venosum)  is 
an  example  of  another  type,  with 
only  one  kind  of  flower  in  the  head, 
the  true  ligulate  flower.  The  hawk- 
weed,  or  devil's  paint-brush  (H.  au- 
rantiacum),  is  a  related  species,  which 
is  a  troublesome  weed.  The  dande- 
lion and  prickly  lettuce  are  also 
members  of  the  ligulate-flowered  com- 
posites. 

These  ligulate-flowered  composites 
are  now  usually  separated  from  the 
other  composites  as  a  distinct  family 
(the  chicory  family)  Cichoriaceae, 
which  stands  just  before  the  Com- 
positae. 

SUGGESTIONS   FOR   STUDY   OF  THE   DANDELION. 

1188.  The  dandelion  (Taraxacum  dens  leonis). 

The  entire  plant. — Note  the  very  short  stem  (the  plant  is  sometimes  said 
to  be  acaulescent,  but  it  has  a  short  stem).  Note  the  thick  root;  the  posi- 
tion of  the  leaves  (often  called  radicle  leaves  because  of  their  position  on 
the  short  stem  so  near  the  roots).  Sketch  a  leaf  to  show  its  form. 

The  inflorescence. — What  is  the  kind  of  inflorescence?  Note  the  leaf- 
less stem  (flowering  scape)  which  bears  the  head  of  flowers.  Cut  across 
the  stem  and  split  it,  and  then  describe  its  character. 

The  involucre. — How  many  whorls  of  bracts  are  there  in  the  involucre  ? 
Comparing  plants  in  flower  and  at  different  stages  of  maturity,  describe 
the  different  positions  of  the  involucre. 

The  flowers. — Are  all  the  flowers  strap-shaped  ?  Note  the  ligula.  Why 
is  it  a  true  ligula?  Describe  and  sketch  a  single  flower. 

The  calyx. — What  represents  the  calyx?  Describe  the  free  portion,  or 
limb.  What  is  the  insertion  of  the  calyx? 


Fig.  SQ2. 

Rattlesnake- weed  (Hieracium 
venosum). 


DICOTYLEDONS:    CAMPANULALES.  7<DI 

The  corolla. — What  represents  the  corolla,  and  how  many  petals  are 
indicated  ? 

The  stamens. — What  is  the  relation  of  the  stamens  to  each  other?  What 
is  the  name  applied  to  such  stamens?  Sketch  a  few  of  the  stamens  to 
show  their  relation  to  each  other. 

The  pistil. — How  many  carpels  are  represented  in  the  pistil  ?  What  is 
the  indication  of  this?  What  is  the  relation  of  the  different  sets  of  the 
flower  to  each  other,  and  what  is  their  insertion  ?  Give  the  names  applied 
to  these  different  relations. 

The  fruit. — Comparing  the  different  stages  of  the  ripening  seed,  describe 
the  changes  which  take  place  in  the  different  parts  of  the  flower  and  head. 
What  parts  of  the  flower  are  united  in  the  fruit?  What  is  such  a  fruit 
called?  How  many  seeds  in  the  fruit? 

Seed  distribution. — How  are  seeds  of  the  dandelion  adapted  for  seed 
distribution?  Take  a  head  of  ripe  seeds,  and  blow  upon  it.  Note  how 
the  seeds  float;  observe  which  end  falls  first  upon  the  ground  (see  Chapter 
XLV,  Seed  Dispersal). 

Cross-pollination. — In  some  of  the  composites,  as  in  the  daisy  or  in  the 
sunflower,  determine  what  provision  is  present  for  cross-pollination.  Do 
all  the  flowers  "blossom"  at  the  same  time  in  a  single  head?  Which  ones 
blossom  first?  Do  the  stamens  ripen  and  emerge  from  the  throat  of  the 
corolla  at  the  same  time  as  the  stigma  in  the  same  flower?  Why?  Com- 
pare the  dandelion  in  these  respects. 

Material. — Entire  plants,  with  flowers  (they  can  be  obtained  all  through 
the  spring);  heads  of  fruit  in  different  stages  of  maturity. 

1189.  The  extent  to  which  the  union  of  the  parts  of  the  flower  has  been 
carried  in  the  composites,  and  the  close  aggregation  of  the  flowers  in  a  head, 
represent  the  highest  stage  of  evolution  reached  by  the  flowers  of  the  angio- 
sperms.  The  composites  stand  just  above  the  bell-flowers  and  lobelias, 
at  the  termination  of  a  series  (see  paragraphs  1221,  1222).  The  teasels 
show  a  relationship  to  the  composites  in  the  aggergation  of  the  flowers 
in  a  head.  But  the  consolidation  of  the  parts  of  the  flower  has  not  been 
carried  so  far,  and  the  flowers  are  each  separated  by  an  "epicalyx"  in 
the  form  of  a  minute  cup-shaped  involucre.  The  teasels  stand  at  the 
termination  of  another  series  in  which  are  the  lonicera  and  valerian  families. 
The  gynoecium  of  the  composites  presents  a  highly  specialized  structure. 
The  ovary  is  plainly  made  up  of  two  carpels,  as  shown  by  the  two  styles 
and  the  internal  structure,  but  it  becomes  reduced  to  a  one-seeded  achene. 
From  the  five  carpels  in  the  pyrolas  to  the  composites  there  is  a  gradual 
tendency  toward  reduction  in  number  of  the  carpels  to  two,  and  in  the 
composites  the  highest  specialization  is  reached  in  the  consolidation  of 
these  into  one  achene  in  fruit. 


CHAPTER  LXVI. 

CLASSIFICATION    OF   THE   ANGIOSPERMS. 
Group  Angiospermae. 

I.    CLASS   MONOCOTYLEDONES. 

1190.  Order  Pandanales.— Aquatic   or  marsh   plants.    The 
cattail  flags  (Typha)  and  the  bur-reeds  (Sparganium) ,  each  rep- 
resenting a  family.     The    name    of  the    order    is  taken  from 
the  tropical   genus   Pandanus  (the   screw-pine   often   grown   in 
green-houses). 

1191.  Order  Naiadales. — Aquatic   or    marsh    herbs.     Three 
families  are  mentioned  here. 

The  pond  weed  family  (Naiadaceae),  named  after  one  genus, 
Naias.  The  largest  genus  is  Potamogeton,  the  species  of  which 
are  known  as  pondweeds.  Ruppia  occidentalis  occurs  in 
saline  ponds  in  Nebraska,  and  R.  maritima  along  the  seacoast 
and  in  saline  districts  in  the  interior. 

The  water-plantain  family  (Alismaceae)  includes  the  water- 
plantain  (Alisma)  and  the  arrow-leaves  (Sagittaria). 

The  tape-grass  family  (Vallisneriaceae)  includes  the  tape-grass, 
or  eel-grass  (the  curious  Vallisneria  spiralis). 

1192.  Order  Graminales. — Two  families. 

The  grass  family  (Gramineae),  the  grasses  and  grains. 
The  sedge  family  (Cyperaceae),  the  sedges. 

1193.  Order  Palmales,  with  one  family,  Palmaceae,  includes 
the  palms,  abundant  in  the  tropics  and  extending  into  Florida. 
Cultivated  in  greenhouses. 

702 


CLASSIFICATION.  703 

1194.  Order  Arales.     (See  Chapter  LX.) 

The  arum  family  (Araceae).  Flowers  in  a  fleshy  spadix.  Ex- 
amples: Indian  turnip  (Arisaema),  sweet-flag  (Acorus),  skunk- 
cabbage  (Spathyema). 

The  duckweed  family  (Lemnaceae).  (Examples:  Lemna, 
Spirodela,  Wolfna.  See  paragraphs  51-53.) 

1195.  Order   Xyridales,  from  the   genus  Xyris,   the  yellow- 
eyed   grass   family    (Xyridaceae).     Species   mostly   tropical,   but 
a  few  in  North  America.     Other  examples  are  the  pipewort 
family    (Eriocaulaceae,   example,    Eriocaulon   septangulare) ,  the 
pineapple  family   (Bromeliaceae,   example,  the    pineapple   culti- 
vated in  Florida) ;  the  Florida  moss  or  hanging  moss  (Tillandsia 
usneoides) ;   the    spiderwort    family   (Commelinaceae),  including 
the  spiderwort  (Tradescantia,  several  species  in  North  America) ; 
the  pickerel- weed  family  (Pontederiaceae) ,  including   the  genus 
Pontederia  in  borders  of  ponds  and  streams. 

1196.  Order   Liliales.— (See  Chapter   LIX).     Some   of   the 
families  are  as  follows: 

The  rush  family  (Juncaceae,  example,  Juncus),  with  many 
species,  plants  of  usually  swamp  habit. 

The  lily  family  (Liliaceae,  examples:  Lilium,  Allium  =  Onion, 
Erythronium,  Yucca). 

The  iris  family  (Iridaceae,  examples:  Iris,  the  blue-flag, 
fleur-de-lis,  etc.). 

The  lily-of-the-valley  family  (Convallariaceae,  examples:  lily- 
of-the-valley,  Trillium,  etc.) 

The  amaryllis  family  (Amaryllidaceae,  examples:  Narcissus, 
the  daffodil;  Cooperia,  in  southwestern  United  States). 

1197.  Order   Scitaminales.— This  order    includes    the    large 
showy  cultivated  Canna  of  the  canna  family. 

1198.  Order  Orchidales.     Example,  the  orchid  family  (Orchi- 
daceae,  see  Chapter  LIX)  with  Cypripedium,  Orchis,  etc. 


704  ORDERS   OF  ANGIOSPERMS. 


II.  CLASS  DICOTYLEDONES. 

SERIES  i.  CHORIPETAL.E.  Petals  wanting  (Apetalse,  or 
Archichlamydae  of  some  authors),  or  present  and  distinct  from 
one  another  (Polypetalae,  or  MetacHamydae). 

1199.  Order    Casuarinales,   confined    to  tropical    seacoasts 
(example,  Casuarina). 

1200.  Order  Piperales  includes  the  lizard's-tail  family  (Sau- 
ruraceae),  Saururus  cernuus,  lizard's-tail,  in  the  eastern  United 
States. 

1201.  Order  Salicales.— Shrubs  or  trees,  flowers  in  aments. 
Includes  the  willows  and  poplars   (Salix  and  Populus  of  the 
willow  family,   Salicaceae.     See   Chapter  LXI.) 

1202.  Order  Myricales.— Shrubs  or  small  trees.     Includes  the 
sweet-gale  (Myrica  gale)  in  wet  places  in  northern  United  States 
and  British  North  America,  Myrica  cerifera  forming  thickets 
on  sand-dunes    along    the  Atlantic  coast,   and  the  sweet-fern 
(Comptonia    peregrina  =  C.  asplenifolia)  in  the  eastern  United 
States  in  dry  soil  of  hillsides. 

1203.  Order  Leitneriales. — Shrubs  or  trees.    Includes  the  cork- 
wood, Leitneria  floridana  (Leitneriaceae). 

1204.  Order  Juglandales.— Trees,  staminate  flowers  in  aments. 
The  walnut  family  (Juglandaceae,  examples:  walnut,  butternut, 
etc.    Juglans;    hickory,  Hicoria  =  Carya. 

1205.  Order  Fagales.— Trees  and  shrubs.    Flowers  in  aments, 
or  the  pistillate  ones  with  an  involucre  which  forms  a  cup  in 
fruit,  as  in  the  acorn  of  the  oak. 

The  birch  family  (Betulaceae,  examples:  Betula,  birch;  Cory- 
lus,  hazelnut;  Alnus,  alder,  etc.). 

The  beech  family  (Fagaceae  =  Cupuliferae,  examples:  Fagus, 
beech;  Castanea,  chestnut;  Quercus,  oak.  See  Chapter  LXI). 

1206.  Order  Urticales. — Trees,  shrubs,  or  herbs.     Examples: 
the  elm  family  (Ulmaceae.     See   Chapter  LXII),  the  mulberry 
family  (Moraceae),  and  the  nettle  family  (Urticaceae). 

1207.  Order  Santalales,  herbs  or  shrubs,  mostly  parasitic. 


CLASSIFICA  TICK. 

The  mistletoe  family  (Loranthaceae),  with  the  American 
mistletoe  (Phoradendron  flavescens),  parasitic  on  deciduous 
trees  in  the  South  Atlantic,  Central,  and  Gulf  States  (N.  J. 
to  Ind.  Ter.). 

The  sandalwood  family  (Santalaceae,  example,  the  bastard 
toad-flax,  Comandra  umbellata),  widely  distributed  in  North 
America. 

1208.  Order  Aristolochiales.— Herbs  or  vines    with    heart- 
shaped  or  kidney-shaped  leaves.     The  birthwort  family  (Aris- 
tolochiaceae,    example,    Aristolochia    serpentaria,   the    Virginia 
snake-root,  eastern  United    States;    wild  ginger,  or   heart-leaf, 
Asarum  canadense,  eastern  North  America.) 

1209.  Order  Polygonales.— Examples:  the  buckwheat  family 
(Polygonaceae),  including  buckwheat  (Fagopyrum),  and  numer- 
ous species  of  Polygonum,  known  as  smartweed,  water-pepper, 
tear-thumb,  bindweed,  knotweed,  prince's-feather,  etc. 

1210.  Order  Chenopodiales. — Herbs.    There  are  several  fam- 
ilies; one  of  the  largest  is  the  goosefoot  family  (Chenopodiaceae). 
The  genus  Chenopodium  includes  many  species,  known  as  goose- 
foot,  lamb's-quarters,  etc.     Here  belong  also  the  Russian  thistle 
(Salsola  tragus)  and  the  saltwort  (S.  kali).     The  former  is  some- 
times a  troublesome  weed  in  the  central  and  western  United  States, 
naturalized  from  Europe.     The  latter  occurs  along  the  Atlantic 
coast  on  seabeaches.       Atriplex  occurs  in  salty  or  alkaline  soil, 
also   the   glasswort    (Salicornia   herbacea),    the   bugseed    (Cori- 
spermum).    The  pokeweed  family  (Phytolaccaceae) ,  the  Amaranth 
family    (Amaranthaceae) ,    the    purslane    family    (Portulacaceae, 
including  the  purslane  or  "pursley,"   Portulaca  oleracea,  and 
the  spring-beauty,   Claytonia  virginica),  and    the    pink   family 
(Caryophyllaceae),  belong  here. 

1211.  Order  Ranales. — Herbs,  shrubs,   or  trees.      Examples 
are: 

The  water-lily  family  (Nymphaeaceae) ,  with  the  yellow  water-lily 
(Nymphaea  advena  =  Nuphar  advena)  and  the  white  water-lily 
(Castalia  odorata= Nymphaea  odorata). 

The    magnolia    family    (Magnoliaceae),    including    the    mag- 


700  ORDERS   OF  ANGIOSPERMS. 

nolias  (Magnolia)  and  the  tulip-tree  (Liriodendron).  The  crow- 
foot family  (Ranunculaceae),  with  the  buttercups,  hepatica,  clem- 
atis, etc.  (See  Chapter  LXII). 

1212.  Order  Papaverales. — Mostly  herbs.     Examples  are: 
The  poppy   family   (Papaveraceae),   including   the  opium  or 

garden  poppy  (Papaver  somniferum),  the  blood-root  (Sangui- 
naria  canadensis),  the  Dutchman' s-breeches  (Bicuculla  cucul- 
laria  =  Dicentra  cucullaria),  squirrel' s-corn  (Bicuculla  canaden- 
sis =D.  canadensis). 

The  mustard  family  (Cruciferae) ,  including  the  tooth  wort 
(Dentaria),  .  shepherd's-purse  (Bursa  bursa-pastoris  =  Capsella 
bursa-pastoris,  see  Chapter  LXII),  the  cabbage,  turnip,  etc. 

1213.  Order  Sarraceniales.— Insectivorous  plants. 

The  pitcher-plant  family  (Sarraceniaceae).  Examples:  Sarra- 
cenia  purpurea,  the  pitcher-plant,  in  peat-bogs,  northern  and 
eastern  North  America. 

The  sundew  family  (Droseraceae) .  Examples:  Drosera  rotun- 
difolia,  and  other  sundews. 

1214.  Order   Resales. — Herbs,    shrubs   or   trees.     Seventeen 
families  are  given  in  the  eastern  United  States.     Examples: 

The  riverweed  family  (Podostemaceae) ,  containing  the  river- 
weed  (Podostemon). 

The  saxifrage  family  (Saxifragaceae) ,  containing  a  number  of 
species.  Example,  Saxifraga  virginiensis. 

The  gooseberry  family  (Grossulariaceae),  including  the  wild 
and  the  cultivated  gooseberry. 

The  witch-hazel  family  (Hamamelidaceae),  including  the 
witch-hazel  (Hamamelis),  in  eastern  North  America,  and  the 
sweet-gum  (Liquidambar  styraciflua) . 

The  plane-tree  family  (Platanaceae),  with  the  plane-tree,  or 
buttonwood  (Platanus  occidentalis),  eastern  North  America. 
(Other  species  occur  in  western  United  States.) 

The  rose  family  (Rosaceae),  including  roses,  spiraeas,  rasp- 
berries, strawberries,  the  shrubby  cinquefoil  (Dasiphora  fruti- 
cosa),  etc. 

The  apple  family  (Pomaceae),  including  the  apple,  mountain- 


CLASSIFICATION.  7O/ 

ash,  pear,  June-berry  (or  shadbush,  also  service-berry),  the  haw- 
thorns (Crataegus,  see  Chapter  LXIII). 

The  plum  family  (Drupaceae),  including  the  cherries,  plums, 
peaches,  etc. 

The  pea  family  (Papilionaceae) ,  including  the  pea,  bean, 
clover,  vetch,  lupine,  etc.,  a  very  large  family. 

1215.  Order   Geraniales. — Herbs,    shrubs,    or    trees.     Nine 
families  in  the  eastern  United  States.     Examples: 

The  geranium  family  (Geraniaceae),  with  the  cranesbill  (Gera- 
nium maculatum)  and  others. 

The  wood-sorrel  family  (Oxalidaceae),  with  the  wood-sorrel 
(Oxalis  acetosella)  and  others. 

The  flax  family  (Linaceae).  Example,  flax  (Linum  vul- 
garis). 

The  spurge  family  (Euphorbiaceae).  Plants  with  a  milky 
juice,  and  curious,  degenerate  flowers.  Examples:  the  castor- 
oil  plant  (Ricinus),  the  spurges  (many  species  of  Euphorbia). 

1216.  Order   Sapindales. — Mostly  trees  or  shrubs.     Twelve 
families  in  the  eastern  United  States.     Examples: 

The  sumac  family  (Anacardiaceae),  containing  the  sumacs  in 
the  genus  Rhus.  (Examples:  the  poison-ivy  (R.  radicans),  a 
climbing  vine,  in  thickets  and  along  fences,  in  eastern  United 
States.  Sometimes  trained  over  porches.  The  poison  -  oak 
(R.  toxicodendron) ,  a  low  shrub.  Poison-sumac  or  poison-alder 
(R.  vernix=R.  venenata),  sometimes  called  "thunderwood," 
or  dogwood,  is  a  large  shrub  or  small  tree,  very  poisonous.  The 
smoke-tree  (Cotinus  cotinoides)  belongs'  to  the  same  family,  and 
is  often  planted  as  an  ornamental  tree.  The  maple  family  (Ace- 
raceae),  including  the  maples  (Acer,  see  Chapter  LXIII). 

The  buckeye  family  (Hippocastanaceae) ,  including  the  horse- 
chestnut  (/Esculus  hippocastanum),  much  planted  as  a  shade 
tree  along  streets.  Also  there  are  several  species  of  buckeye  in 
the  same  genus. 

The  jewelweed  family  (Balsaminaceae),  including  the  touch- 
me-not  (Impatiens  biflora  and  aurea)  in  moist  places.  The 
garden  balsam  (Imp.  balsamea)  also  belongs  here. 


7O8  ORDERS   Of  ANGIOSPERMS. 

1217.  Order  Rhamnales. — Shrubs,  vines,  or  small  trees.   There 
are  two  families,  the  buckthorn  (Rhamnaceae),  the  grape  family 
(Vitaceae),  including  the  grapes  (Vitis),  the  American  ivy  (Par- 
thenocissus    quinquefolia=Ampelopsis    quinquef olia) ,   in  woods 
and  thickets,  eastern   North  America,  and  much  planted  as  a 
trailer  over  porches.     The   Japanese   ivy    (P.   tricuspidata=A. 
veitchii)   used  as  a  trailer  on   the    sides   of   buildings   belongs 
here. 

1218.  Order  Malvales. — Herbs,  shrubs,  or  trees. 

The  linden  family  (Tiliaceae).  Example,  the  basswood  or 
American  linden  (Tilia  americana.) 

The  mallow  family  (Malvaceae),  including  the  hollyhock,  the 
mallows,  rose  of  Sharon  (Hibiscus),  etc. 

1219.  Order  Parietales,  with  seven  families  in  the  eastern 
United  States.      The  St.-John's-wort  (Hypericum)  and   the  vio- 
lets each  represent  a  family.      The  violets  (Violaceae)  are  well- 
known  flowers. 

1220.  Order  Opunliales. — These  include  the  cacti  (Cactaceae), 
chiefly  growing  in  the  dry  or  desert  regions  of  America. 

1221.  Order    Thymeleales,    with     two     families    and     few 
species. 

1222.  Order    Myrtales. — Land,    marsh,    or    aquatic    plants. 
The    most    conspicuous  are    in    the    evening    primrose    family 
(Onagraceae),  including  the  fireweeds,  or  willow  herbs  (Epilobium), 
and    the    evening   primrose    (Onagra   biennis  =  (Enothera  bien- 
nis). 

1223.  Order  Umbellales. — Herbs,  shrubs,  or  trees,  flowers  in 
umbels. 

The  ginseng  family  (Araliaceae).  This  includes  the  spikenards 
and  sarsaparillas  in  the  genus  Aralia,  and  the  ginseng  (or  "  sang"), 
Panax  quinquef olium. 

The  carrot  family  (Umbelliferae).  This  family  includes  the 
wild  carrot  (Daucus  carota),  the  poison-hemlock  (Cicuta),  the 
cultivated  carrot  and  parsnip,  and  a  large  number  of  other  genera 
and  species. 

The  dogwood  family   (Cornaceae).     The  flowering  dogwood 


CLASSIFICA  TION.  709 

(Cornus  florida),  abundant  in  eastern  North  America,  is  an 
example. 

SERIES  2  GAMOPETAL.E  (  =  Sympetake  or  Metachla- 
mydae) .  Petals  partly  or  wholly  united,  rarely  separate  or  wanting. 

1224.  Order  Ericales.— There  are  six  families  in  eastern 
United  States.  Examples: 

The  wintergreen  family  (Pyrolaceae),  including  the  shin-leaf 
(Pyrola  elliptica). 

The  Indian-pipe  family  (Monotropaceae),  with  the  Indian- 
pipe  (Monotropa  uniflora)  and  other  humus  saprophytes.  (See 
paragraphs  182-191.) 

The  heath  family  (Ericaceae).  Examples:  Labrador  tea 
(Ledum),  in  bogs  and  swamps  in  northern  North  America. 
The  azaleas,  with  several  species  widely  distributed,  are  beauti- 
ful flowering  shrubs,  and  many  varieties  are  cultivated.  The 
rhododendrons  are  larger  with  larger  flower-clusters,  also  beau- 
tiful flowering  shrubs.  R.  maximum  in  the  Alleghany  Moun- 
tains and  vicinity,  from  Nova  Scotia  to  Ohio  and  Georgia.  R. 
catawbiense,  usually  at  somewhat  higher  elevations,  Virginia 
to  Georgia.  The  mountain  laurel  (Kalmia  latifolia)  and 
other  species  rival  the  rhododendrons  and  azaleas  in  beauty. 
The  trailing  arbutus  (Epigaea  repens)  in  sandy  or  rocky  woods  is 
a  well-known  small  trailing  shrub  in  eastern  North  America. 
The  sourwood  (Oxydendrum  arboreum)  is  a  tree  with  white 
racemes  of  flowers  in  August,  and  scarlet  leaves  in  autumn. 
The  spring  or  creeping  wintergreen  (Gaultheria  procumbens)  is 
a  small  shrub  with  aromatic  leaves,  and  bright  red  spicy  berries. 

The  huckleberry  family  (Vaccinaceae)  includes  the  huckle- 
berries (example,  Gaylussacia  resinosa,  the  black  or  high- 
bush  huckleberry,  eastern  United  States),  the  mountain  cran- 
berry (Vitis-Idaea  vitisidaea=Vaccinium  vitisidaea)  in  the  north- 
ern hemisphere;  the  bilberries  and  blueberries  (of  genus  Vacci- 
nium);  the  cranberries  (examples:  the  large  American  cranberry, 
Oxycoccus  macrocarpus  and  the  European  cranberry,  Oxycoc- 
cus  oxycoccus,  in  cold  bogs  of  northern  North  America,  the 
latter  also  in  Europe  and  Asia). 


710  ORDERS  OF  ANGIOSPERMS. 

1225.  Order  Primulales.— Two  families  here.     The  primrose 
family  (Primulaceae)  contains  the  loosestrifes  (Steironema),  star- 
flower  (Trientalis),  etc. 

1226.  Order  Ebenales. — Of  the  four  families,  the  ebony  fam- 
ily (Ebenaceae)  contains  the '  well-known  persimmon  (Diospyros 
virginiana)  and  the  storax  family  (Styracaceae)  with   the  silver- 
bell,  or  snowdrop  tree  (Mohrodendron  carolinum). 

1227.  Order  Gentianales. — Herbs,    shrubs,    vines,    or    trees. 
Six  families  in  the  United  States. 

The  olive  family  (Oleaceae)  includes  the  common  lilac  (Syrin- 
ga),  the  ash  trees  (Fraxinus),  the  privet  (Ligustrum). 

The  gentian  family  (Gentianaceae)  among  other  genera  in- 
cludes the  gentians  (Gentiana). 

The  milkweed  family  (Asclepiadaceae)  contains  plants  mostly 
with  a  milky  juice.  Asclepias  with  many  species  is  one  of  the 
most  prominent  genera. 

1228  Order  Polemoniales. — Mostly  herbs,  rarely  shrubs  and 
trees.  Fifteen  families  in  the  eastern  United  States. 

The  morning-glory  family  (Convolvulaceae)  includes  the 
bindweeds  (Convolvulus),  the  morning-glory  (Ipomaea),  etc. 

The  dodder  family  (Cuscutaceae)  includes  the  dodders,  or 
"  love-vines."  There  are  nearly  thirty  species  in  the  United 
States.  The  stems  are  slender  and  twine  around  other  plants 
upon  which  they  are  parasitic  (see  paragraph  179). 

The  phlox  family  (Polemoniaceae) .  The  most  prominent 
genus  is  Phlox.  Over  forty  species  occur  in  North  America. 

The  borage  family  (Boraginaceae)  includes  the  heliotrope 
(Heliotropium),  the  hound' s-tongue  (Cynoglossum),  the  forget- 
me-not  (Myosotis),  and  others. 

The  vena  n  family  (verbenaceae)  contains  the  verbenas. 
The  mint  family  (Labiatae)  contains    the  mints  (Mentha),  skull- 
cap (Scutellaria),  dead-nettles  (Lamium). 

The  potato  family  (Solanaceae)  includes  the  ground-cherry 
(Physalis),  the  nightshades  (Solanum),  the  tomato  (Lycoper- 
sicon),  tobacco  (Nicotiana). 

The  figwort  family  (Scrophulariaceae)   includes  the  common 


CLA  SSIFICA  TION.  7 1 1 

mullein  (Verbascum) ,  the  monkey-flower  (Mimulus),  the  toad' 
flax  (Linaria),  turtle' s-head  (Chelone),  and  many  other  genera 
and  species. 

The  bladderwort  family  (Lentibulariaceae)  includes  the  curi- 
ous bog  or  aquatic  plants  with  finely  dissected  leaves,  and  with 
bladders  in  which  insects  are  caught  (Utricularia). 

The  trumpet-creeper  family  (Bignoniaceae)  includes  the  trunv 
pet-creeper  (Bignonia),  the  catalpa  tree,  and  others. 

1229  Order  Plantaginales  with  one  family  (Plantaginaceae) 
includes  the  plantains  (Plantago). 

1230.  Order  Rubiales  with  three  families  is  represented  by 
The  madder  family  (Rubiaceae)  with  the  bluets  (Houstonia), 

the  button-bush  (Cephalanthus),  the  partridge-berry  (Mitchella), 
the  bedstraws  (Galium),  etc. 

The  honeysuckle  family  (Caprifoliaceae)  with  the  elder  (Sam- 
bucus),  the  arrowwoods  and  cranberry  trees  (Viburnum),  the 
honeysuckles  (Lonicera),  etc. 

1231.  Order  Valerianales  with  two  families  includes 

The  teasel  family  (Dipsacaceae).  Example,  Fuller's  teasel 
(Dipsacus). 

1232.  Order    Campanulales   with   five   families,    the   corolla 
usually  gamopetalous. 

The  gourd  family  (Cucurbitaceae)  includes  the  pumpkin, 
squash,  melon,  and  a  few  feral  species.  Example,  the  star- 
cucumber  (Sicyos  angulatus),  in  moist  places  in  eastern  and 
middle  United  States. 

The  bell-flower  family  (Campanulaceae)  includes  the  hare- 
bells or  bell-flowers  (Campanula),  the  lobelias  (example,  Lobelia 
cardinalis,  the  cardinal-flower),  etc. 

The  chicory  family  (Cichoriaceae)  includes  the  chicory  or 
succory  (Cichorium  intybus,  known  also  as  blue-sailors),  the 
oyster-plant  or  salsify  (Tragopogon  porrifolius) ,  the  dandelion 
(Taraxacum  taraxacum =T.  densleonis),  the  lettuce  (Lactuca), 
the  hawkweed  (Hieraceum)  (see  paragraph  1177),  and  others. 

The  ragweed  family  (Ambrosiaceae)  includes  the  ragweeds 
(Ambrosia),  the  cockle-bur  (Xanthium),  and  others. 


712  ORDERS     OF  ANGIOSPERMS. 

The  thistle  family  (Compositae)  includes  the  thistle  (Carduus), 
asters  (Aster),  goldenrods  (Solidago),  sunflowers  (Helianthus) , 
eupatoriums  or  joepye- weeds,  thorough  worts  (Eupatorium), 
cone-flowers  or  black-eyed  Susans  (Rudbeckia),  tickseed  (Core- 
opsis), bur-marigold  or  beggar-ticks  or  devil's-bootjack  (Bidens), 
chrysanthemums,  etc. 

Absorption  by  aquatic  plants  through  roots  (see  paragraph  952). — 
Aquatic  plants  which  are  rooted  to  the  soil  in  a  number  of  cases  have  been 
found  to  have  root  hairs.  Experiment  has  demonstrated  in  these  cases 
that  mineral  foods  are  largely  taken  from  the  soil  and  not  from  the  sur- 
rounding water.  Examples  of  such  plants  are  Vallisneria  spiralis,  Ranun- 
culus aquatilis,  Elodea  canadensis,  Potamogeton  perfoliatus.  The  latter 
made  480  per  cent  better  growth  when  rooted  in  soil  than  when  rooted  in 
sand.  Such  plants,  therefore,  taking  their  mineral  food  from  the  soil, 
when  they  decay  increase  the  amount  of  food  for  the  plankton  or  floating 
plants,  or  those  merely  anchored  but  without  well-developed  roots  or  root 
hairs.  See  Pond,  Raymond  H.,  Biological  relation  of  aquatic  plants  to 
the  substratum,  U.  S.  Fish  Commission  Report  for  1903,  pp.  483-526, 
1905.  Also,  How  rooting  aquatic  plants  influence  the  nutrition  of  the 
food  fishes  of  our  Great  Lakes,  Pop.  Sci.  Month.,  pp.  251,  254,  5  figures 
in  text,  March  1906. 
To  prepare  Fehling's  solution. — Make  up  two  stock  solutions  as  follows: 

(  Copper  sulphate 34. 639  grams. 

(  Distilled  water 500  cc. 

C  Sodium  hydroxide  (caustic  soda  sticks) 50  grams. 

B    <  Rochelle  salts 1 73  grams. 

(  Distilled  water 500  cc. 

When  ready  to  use,  prepare  Fehling's  solution  by  mixing  equal  volumes 
of  A  and  B.  If  the  Fehling's  solution  is  old,  or  has  sediment,  bring  it  to 
boil  for  a  minute  or  two  and  filter. 

Another  formula  for  the  stock  solutions  is  as  follows: 

(  Copper  sulphate 9  grams. 

(  Distilled  water 250  cc. 

Potassium  hydroxide  (caustic  potash  sticks) 30  grams. 

Distilled  water 250  cc. 

Rochelle  salts 43  grams. 

Distilled  water 250  cc. 

When  ready  to  use,  make  Fehling's  solution  by  taking  equal  volumes 
of  each  i,  2  and  3,  and  to  the  mixture  add  an  equal  volume  of  dis- 
tilled water.  If  old  or  there  is  a  precipitate,  boil  and  filter. 


APPENDIX. 

COLLECTION  AND  PRESERVATION  OF  MATERIAL. 

Spirogyra  may  be  collected  in  pools  where  the  water  is  pres- 
ent for  a  large  part  of  the  year,  or  on  the  margins  of  large 
bodies  of  water.  To  keep  fresh,  a  small  quantity  should  be 
placed  in  a  large  open  vessel  with  water  in  a  cool  place  fairly 
well  lighted.  In  such  places  it  may  be  kept  several  months  in 
good  condition. 

Mucor  may  be  obtained  by  placing  old  bread,  etc.,  or  horse 
dung,  in  a  moist  covered  vessel.  In  the  course  of  a  week  there 
should  be  an  abundance  of  the  mycelium  and  gonidia.  From 
this  material  cultures  may  be  made,  if  desired,  in  nutrient  gela- 
tin or  nutrient  agar. 

Saprolegnia,  or  water  mould,  can  be  used  for  a  study  of  pro- 
toplasm. Collect  several  dead  house  flies  from  window  sills  of 
neglected  rooms.  Immerse  them  in  alcohol,  then  rinse  in 
water  to  remove  the  alcohol.  Then  throw  them  in  vessels  of 
water  containing  freshly  collected  algae  from  several  different 
places.  In  the  course  of  a  week  there  should  be  a  tuft  of  whit- 
ish threads  of  the  water  mould  surrounding  the  fly. 

Nitella  is  obtained  in  rather  deep  pools  or  ponds,  or  in  slow- 
running  water,  at  a  depth  of  one  to  three  feet  usually. 

Stamen  hairs  of  tradescantia  can  usually  be  obtained  in 
greenhouses  from  flower  buds  just  ready  to  open  or  just  after 
opening. 

(Edogonium  is  often  found  in  floating  mats  in  ponds,  or  on 
the  margins  of  slow-running  streams,  or  of  lakes.  Frequently 
it  is  attached  to  other  aquatic  plants.  Fruiting  plants  can  be 

713 


714  APPENDIX. 

detected  by  certain  of  the  cells  being  rounded  and  broader  than 
others,  and  some  of  them  at  least  usually  containing  the  spores, 
a  single  spore  nearly  or  quite  filling  the  large  cell,  or  oogonium. 
When  it  cannot  be  studied  fresh  it  may  be  preserved  in  2% 
formalin  or  in  70$  alcohol,  first  placing  it  successively  in  25$ 
and  50$  alcohol  for  a  few  hours. 

Some  species  of  vaucheria  occur  in  places  frequented  by 
oedogonium  or  spirogyra,  while  others  occur  in  running  water, 
or  still  others  on  damp  ground.  Frequently  fine  specimens  of 
vaucheria  in  fruit  may  be  found  during  the  winter  growing  on 
the  soil  of  pots  in  greenhouses.  The  jack-in-the-pulpit,  also 
known  as  Indian  turnip,  growing  in  damp  ground  I  have  found 
when  potted  and  grown  in  the  conservatory  yields  an  abundance 
of  the  vaucheria,  probably  the  spores  of  the  alga  having  been 
transferred  with  the  soil  on  the  plants.  When  material  cannot 
be  obtained  fresh  for  study,  it  may  be  preserved  in  advance  in 
formalin  or  alcohol  as  described  for  redogonium. 

Coleochsete  scutata  is  not  so  common  as  the  oedogonium, 
spirogyra,  or  vaucheria.  But  it  may  be  sometimes  found  with 
the  small  circular  green  disks  adhering  to  rushes,  grasses,  or 
Other  aquatic  plants  in  large  ponds  or  on  the  margins  of  lakes. 
When  found  it  is  well  to  make  permanent  mounts  of  material 
killed  in  formalin,  either  in  glycerine  or  glycerine  jelly. 

Wheat  rust. — The  cluster-cup  stage  may  be  collected  in  May 
or  June  on  the  leaves  of  the  barberry.  Some  of  the  affected 
leaves  may  be  dried  between  drying-papers.  Other  specimens 
should  be  preserved  in  2%  formalin  or  in  70$  alcohol.  If  the 
cluster  cup  cannot  be  found  on  the  barberry,  other  species  may 
be  preserved  for  study. 

The  uredospore  and  teleutospore  stages  can  usually  be  found 
abundantly  on  wheat  and  oats,  especially  on  late-sown  oats  which 
ripen  in  autumn.  The  affected  leaves  and  stems  may  be  pre- 
served dry. 

The  powdery  mildews  are  common  during  summer  and  au- 
tumn on  a  variety  of  leaves  of  shrubs,  herbs,  and  trees.  They 
can  be  recognized  by  the  mildewed  spots,  or  by  the  numerous 


COLLECTION  AND    PRESERVATION   OF  MATERIAL.  715 

minute  black  specks    on   the   surface   of  the  leaf.      The  leaves 
should  be  preserved  dry  after  drying  under  pressure. 


Liverworts. 

Marchantia. — The  green  thallus  (gametophyte)  of  marchan- 
tia  may  be  found  at  almost  any  season  of  the  year  along  shady 
banks  washed  by  streams,  or  on  the  wet  low  shaded  soil.  Plants 
with  the  cups  of  gemmae  are  found  throughout  a  large  part  of 
the  year.  They  are  sometimes  found  in  greenhouses,  especially 
where  peat  soil  from  marshy  places  is  used  in  potting.  In  May 
and  June  male  and  female  plants  bear  the  gametophores  and 
sexual  organs.  These  can  be  preserved  in  2\%  formalin  or  in 
70$  alcohol.  If  one  wishes  to  preserve  the  material  chiefly  for 
the  antheridia  and  archegonia  a  small  part  of  the  thallus  may  be 
preserved  with  the  gametophores,  or  the  gametophores  alone. 

In  July  the  sporogonia  mature.  When  these  have  pushed  out 
between  the  curtains  underneath  the  ribs  of  the  gametophore, 
they  can  be  preserved  for  future  study  by  placing  a  portion  of 
the  thallus  bearing  the  gametophore  in  a  tall  vial  with  2%  for- 
malin. Plants  with  the  sporogonia  mature,  but  not  yet  pushed 
from  between  the  curtains  on  the  under  side,  can  be  collected  in 
a  tin  box  which  contains  damp  paper  to  keep  the  plants  moist. 
Here  the  sporogonia  will  emerge,  and  by  examining  them  day 
by  day,  when  some  of  the  sporogonia  have  emerged,  these  plants 
can  be  quickly  transferred  to  the  vials  of  formalin  before  the  spo- 
rogonia have  opened  and  lost  their  spores.  In  this  condition  the 
plant  can  be  preserved  for  several  years  for  study  of  the  gross 
character  of  the  sporogonia  and  the  attachment  to  the  gameto- 
phyte. From  some  of  the  other  plants  permanent  mounts  in 
glycerine  jelly  may  be  made  of  the  spores  and  elaters. 

Riccia. — Riccia  occurs  on  muddy,  usually  shaded  ground. 
Some  species  float  on  the  surface  of  the  water.  It  may  be  pre- 
served in  2$  formalin  or  70$  alcohol. 

Cephalozia,  ptilidium,  bazzania,  jungermannia,  frullania,  and 
other  foliose  liverworts  may  be  found  on  decaying  logs,  on  the 


716  APPENDIX. 

trunks  of  trees,  in  damp  situations.  They  may  be  preserved  in 
formalin  or  alcohol.  Some  of  the  material  may  also  be  dried 
under  pressure. 

Mosses  are  easily  found  and  preserved.  Male  and  female 
plants  for  the  study  of  the  sexual  organs  should  be  preserved  in 
formalin  or  alcohol.  In  all  these  studies  whenever  possible  living 
material  freshly  collected  should  be  used. 

Ferns. 

For  the  study  of  the  general  aspect  of  the  ferti  plant,  polypo- 
dium,  aspidium,  onoclea,  or  other  ferns  may  be  preserved  dry 
after  pressure  in  drying  sheets.  A  portion  of  the  stem  with  the 
leaves  attached  should  be  collected.  These  may  be  mounted  on 
stiff  cardboard  for  use.  The  sporangia  and  spores  can  also  be 
studied  from  dried  material,  but  for  this  purpose  the  ferns  should 
be  collected  before  the  spores  have  been  scattered,  but  soon  after 
the  sporangia  are  mature.  But  when  greenhouses  are  near  it  is 
usually  easy  to  obtain  a  few  leaves  of  some  fern  when  the  sporangia 
are  just  mature  but  not  yet  open.  To  prevent  them  from  opening 
and  scattering  the  spores  in  the  room  before  the  class  is  ready  to 
use  them,  immerse  the  leaves  in  water  until  ready  to  make  the 
mounts ;  or  preserve  them  in  a  damp  chamber  where  the  air  is 
saturated  with  moisture. 

For  study  of  the  prothallia  of  ferns,  spores  should  be  caught 
in  paper  bags  by  placing  therein  portions  of  leaves  bearing  ma- 
ture sporangia  which  have  not  yet  opened.  They  should  be 
kept  in  a  rather  dry  but  cool  place  for  one  or  two  months. 
Then  the  spores  may  be  sown  on  well -drained  peat  soil  in  pots, 
and  on  bits  of  crockery  strewn  over  the  surface.  Keep  the  pots 
in  a  glass-covered  case  where  the  air  is  moist  and  the  light  is 
not  strong.  If  possible  a  gardener  in  a  conservatory  should  be 
consulted,  and  usually  they  are  very  obliging  in  giving  sugges- 
tions or  even  aid  in  growing  the  prothallia. 

Lycopodium,  equisetum,  selaginella,  isoetes,  and  other  pteri- 
dophytes  desired  may  be  preserved  dry  and  in  70$  alcohol. 

Pines. — The  ripe  cones  should  be  collected  before  the  seeds 


COLLECTION  AND   PRESERVATION  OF  MATERIAL. 

scatter,  and  be  preserved  dry.  Other  stages  of  the  development 
of  the  female  cones  should  be  preserved  either  in  70$  alcohol  or 
in  2\%  formalin.  The  male  cones  should  be  collected  a  short 
time  before  the  scattering  of  the  pollen,  and  be  preserved  either 
in  alcohol  or  formalin. 

Angiosperms. — In  the  study  of  the  angiosperms,  if  it  is  de- 
sired to  use  trillium  in  the  living  state  for  the  morphology  of  the 
flower  before  the  usual  time  for  the  appearance  of  the  flower  in 
the  spring,  the  root-stocks  may  be  collected  in  the  autumn,  and 
be  kept  bedded  in  soil  in  a  box  where  the  plants  will  be  sub- 
jected to  conditions  of  cold,  etc. ,  similar  to  those  under  which 
the  plants  exist.  The  box  can  then  be  brought  into  a  warm 
room  during  February  or  March,  a  few  weeks  before  the  plants 
are  wanted,  when  they  will  appear  and  blossom.  If  this  is 
not  possible,  the  entire  plant  may  be  pressed  and  dried  for  the 
study  of  the  general  appearance  and  for  the  leaves,  while  the 
flower  may  be  preserved  in  2\%  formalin,  of  course  preserving  a 
considerable  quantity.  Other  material  for  the  study  of  the  plant 
families  of  angiosperms  may  be  preserved  dry,  and  the  flowers 
in  formalin,  if  they  cannot  be  collected  during  the.  season  while 
the  study  is  going  on. 

Demonstrations. — Upon  some  of  the  more  difficult  subjects  in 
any  part  of  the  course,  especially  those  requiring  sections  of  the 
material,  demonstrations  may  be  made  by  the  teacher.  The  ex- 
tent to  which  this  must  be  carried  will  depend  on  the  student's 
ability  to  make  free-hand  sections  of  the  simpler  subjects,  upon 
the  time  which  the  student  has  in  which  to  prepare  the  material 
for  study,  and  the  desirability  in  each  case  of  giving  demostra- 
tions  on  the  minuter  anatomy,  the  structure  of  the  sexual  organs 
and  other  parts,  in  groups  where  the  material  should  be  killed 
and  prepared  according  to  some  methods  of  precision,  now  used 
in  modern  botanical  laboratories.  The  more  difficult  demonstra- 
tions of  this  kind  should  be  made  by  the  instructor,  and  such 
preparations  once  made  properly  can  be  preserved  for  future 
demonstrations.  Some  of  them  may  be  obtained  from  persons 
who  prepare  good  slides,  but  in  such  cases  fancy  preparations  of 


718  APPENDIX. 

curious  structures  should  not  be  used,  but  slides  illustrating  the 
essential  morphological  and  developmental  features.  Directions 
for  the  preparation  of  material  in  this  way  cannot  be  given,  in 
this  elementary  book,  for  want  of  space. 

Method  of  taking  notes,  etc. — In  connection  with  the  prac- 
tical work  the  pupil  should  make  careful  drawings  from  the 
specimens ;  in  most  cases  good  outline  drawings,  to  show  form, 
structure  etc.,  are  preferable,  but  sometimes  shading  can  be 
used  to  good  advantage.  It  is  suggested  that  the  upper  2/3  of 
a  sheet  be  used  for  the  drawings,  which  should  be  neatly  made 
and  lettered,  and  the  lower  part  of  the  page  be  used  for  the 
brief  descriptions,  or  names  of  the  parts.  The  fuller  notes  and 
descriptions  of  the  plant,  or  process,  or  record  of  the  experi- 
ment should  be  made  on  another  sheet,  using  one,  two,  three, 
or  more  sheets  where  necessary.  Notes  and  drawings  should  be 
made  only  on  one  side  of  the  sheet.  The  note-sheets  and  the 
drawing-sheets  for  a  single  study,  as  a  single  experiment,  should 
be  given  the  same  number,  so  that  they  can  be  bound  together 
in  the  cover  in  consecutive  order.  Each  experiment  may  be 
thus  numbered,  and  all  the  experiments  on  one  subject  then 
can  be  bound  in  one  cover  for  inspection  by  the  instructor. 
For  example,  under  protoplasm,  spirogyra  may  be  No.  i,  mucor 
No.  2,  and  so  on.  In  connection  with  the  practical  work  the 
book  can  be  used  by  the  student  as  a  reference  book ;  and  dur- 
ing study  hours  the  book  can  be  read  with  the  object  of  arrang- 
ing and  fixing  the  subject  in  the  mind,  in  a  logical  order. 

The  instructor  should  see  that  each  student  follows  some  well- 
planned  order  in  the  recording  of  the  experiments,  taking  notes, 
and  making  illustrations.  Even  though  a  book  be  at  hand  for 
the  student  to  refer  to,  giving  more  or  less  general  or  specific 
directions  for  carrying  on  the  work,  it  is  a  good  plan  fo^  t^ery 
teacher  to  give  at  the  beginning  of  the  period  of  laboratory 
work  a  short  talk  on  the  subject  for  investigation,  giving  general 
directions.  Even  then  it  will  be  necessary  to  give  each  indi- 
vidual help  in  the  use  of  instruments,  and  in  making  prepara- 
tions for  study,  until  the  work  has  proceeded  for  some  time, 


APPARATUS  AND    GLASSWARE.  719 

when  more  general  directions  usually  answer.  The  author  does 
not  believe  it  a  good  plan  for  the  student  to  have  written, 
minute,  directions  for  preparing  the  plants  and  experiments. 
General  directions  and  specific  help  where  there  is  difficulty, 
until  the  student  learns  to  become  somewhat  independent,  seems 
to  be  a  better  plan. 


APPARATUS   AND   GLASSWARE. 

The  necessary  apparatus  should  be  carefully  planned  and  be 
provided  for  in  advance.  The  microscopes  are  the  most  expen- 
sive pieces  of  apparatus,  and  yet  in  recent  years  very  good  mi- 
croscopes may  be  obtained  at  reasonable  rates,  and  they  are 
necessary  in  any  well  -regulated  laboratory,  even  in  elementary 
work. 

Microscopes.  The  number  of  compound  microscopes  will 
depend  on  the  number  of  students  in  the  class,  and  also  on  the 
number  of  sections  into  which  the  class  can  be  conveniently 
divided.  In  a  class  of  60  beginning  students  I  have  made  two 
sections,  about  30  in  each  section  ;  and  2  students  work  with 
one  microscope.  In  this  way  15  microscopes  answer  for  the 
class  of  60  students.  It  is  possible,  though  not  so  desirable,  to 
work  a  larger  number  of  students  at  one  microscope.  Some  can 
be  studying  the  gross  characters  of  the  plant,  setting  up  appa- 
ratus, making  notes  and  illustrations,  etc.,  while  another  is  en- 
gaged at  the  microscope  with  his  observations. 

The  writer  does  not  wish  to  express  a  preference  for  any  pat- 
tern of  microscope.  It  is  desirable,  however,  to  add  a  little  to 
che  price  of  a  microscope  and  obtain  a  convenient  working 
ou  .  For  example,  a  fairly  good  stand,  two  objectives  (2/3 
and  1/6),  one  or  two  oculars,  a  fine  adjustment,  and  a  coarse 
adjustment  by  rack  and  pinion,  and  finally  a  revolver,  or  nose- 
piece,  for  the  two  objectives,  so  that  both  can  be  kept  on  the 
microscope  in  readiness  for  use  without  the  trouble  of  removing 
one  and  putting  on  another.  Such  a  microscope,  which  I  have 


7  2O  A  PPEND IX. 

found  to  be  excellent,  is  Bausch  &  Lomb's  AAB  (which  they 
recommend  for  high  schools),  costing  about  $25.00  to  $28.00. 
I  have  compared  it  with  some  foreign  patterns,  and  the  cost  of 
these  is  no  less,  duty  free,  for  an  equivalent  outfit.  Of  course, 
one  can  obtain  a  microscope  for  $18.00  to  $20.00  without  some 
of  these  accessories,  but  I  believe  it  is  better  to  have  fewer 
microscopes  with  these  accessories  than  more  without  them. 
Of  the  foreign  patterns  the  Leitz  (furnished  by  Wm.  Krafft, 
411  W.  59th  St.,  N.  Y. )  and  the  Reichert  are  good,  while  Queen 
&  Co.,  Philadelphia,  Pa.,  and  Bausch  &  Lomb,  Rochester, 
N.  Y.,  furnish  good  American  instruments. 

Glass  slips,  3X1  inch ;  and  circle  glass  covers,  thin,  3/4  in. 
diameter. 

Glass  tubing  of  several  different  sizes,  especially  some  about 
$mm  inside  diameter  and  *]mm  outside  measurement,  for  root- 
pressure  experiments. 

Rubber  tubing  to  fit  the  glass  tubing,  and  small  copper  wire 
to  tighten  the  joints. 

Watch  glasses,  the  Syracuse  pattern  (Bausch  &  Lomb),  are 
convenient. 

U  tubes,  some  about  2omm  diameter  and  io—i$cm  long. 
Corks  to  fit. 

Small  glass  pipettes  ( ' '  medicine  droppers  ' ' )  with  rubber 
bulbs. 

Wide-mouth  bottles  with  corks  to  fit.  Reagent  bottles.  (Small 
ordinary  bottles  about  locm  x  4cm  with  cork  stoppers  will  an- 
swer for  the  ordinary  reagents.  The  corks  can  be  perforated 
and  a  pipette  be  kept  in  place  in  each  ready  for  use.  Such 
bottles  should  not  be  used  for  strong  acids.) 

Small  vials  with  corks  for  keeping  the  smaller  preparations  in. 

Small  glass  beakers  or  tumblers. 

A  few  crockery  jars  for  water  cultures. 

Fruit  jars  for  storing  quantities  of  plant  material. 

Glass    graduates;     i    graduated    to    IOOQCC,    i    graduated    to 

IOOCC. 

Funnels,  small   and  medium  (6  and  locm  in  width).     Test 


APPARATUS  AND    GLASSWARE.  J21 

tubes.  A  few  petrie  dishes.  Bell  jars,  a  few  tall  ones  and  a 
few  low  and  broad.  Thistle  tubes.  Chemical  thermometer. 

Balance  for  weighing.  A  small  hand-scale  furnished  by  Eimer 
&  Amend,  205-211  3d  Ave.,  N.  Y.,  is  fairly  good  ($2.00). 

For  pot  experiments,  the  "  Harvard  trip-scale,"  Fairbanks 
Scale  Co.  (about  $6.00). 

Apparatus  stand,  small,  several,  with  clamps  for  holding  test 
tubes,  U  tubes,  etc. 

Agate  trays,  very  shallow,  several  centimeters  long  and  wide. 
Agate  pans,  deep,  for  use  as  aquaria,  etc. ,  with  glass  to  cover. 

Paraffin  or  wax,  for  sealing  joints  in  setting  up  transpiration 
apparatus. 

Mercury,  for  restoration  of  turgidity,  and  for  lifting  power  of 
transpiration. 

Sheet  rubber,  or  prepared  vessels  for  enclosing  pots  to  prevent 
evaporation  of  water  from  surface  during  transpiration  experi- 
ments. 

Litmus  paper,  blue,  kept  in  a  tightly  stoppered  bottle.  Filter 
paper  for  use  as  absorbent  paper.  Lens  paper  (fine  Japanese 
paper)  for  use  in  cleaning  lenses ;  benzine  for  first  moistening 
the  surface,  and  as  an  aid  in  cleaning. 

For  materials  for  culture  solution,  see  Chapter  III. 

REAGENTS. 

Glycerine,  alcohol  of  commercial  (95$)  strength,  formalin  or 
formalose  of  40$  strength,  chloral  hydrate  crystals,  iodine  crys- 
tals, eosin  crystals,  fuchsin  crystals,  potassium  iodide,  potassium 
hydrate,  potash  alum.  It  is  convenient  also  to  have  on  hand 
some  ammonia,  sulphuric  acid,  nitric  acid,  and  muriatic  acid  in 
small  quantity. 

REAGENTS    READY    FOR    USE    AND    FOR     STORING     PLANT    MATERIAL 

IN. 

Alcohol.  Besides  the  95^  strength,  strengths  of  30$,  50$,  and 
70$,  for  killing  material  and  bringing  it  up  to  70$  for  storage. 


722  APPENDIX. 

Formalin.  Usually  about  a  2-*-$  is  used  for  storing  material, 
made  by  taking  97 \  parts  water  in  a  graduate  and  filling  in  2j 
parts  of  the  40$  formalin. 

Salt  solution  5$  ;  sugar  solution  15$  (for  osmosis). 
Iodine    solution.       Weak — to    3000;   distilled  water   add    2 

grams  iodide  of  potassium  ;  to 
this  add  i  gram  iodine  crys- 
tals. 

Strong — use  less  water. 

Eosin.     Alcoholic    solution.       Distilled    water    $occ,    alco- 
hol $occ,  eosin  crystals  ^  gram,    potash  alum  4 
grams. 
Aqueous  solution.    Distilled  water  IOQCC,  eosin  crystals 

i  gram. 

Chloral  hydrate  ;  aqueous  solution,  nearly  sat.  sol. 
Schimper's  solution.      Chloral  hydrate  5  parts,  water  2  parts, 
iodine  to  make  a  strong  color. 

STUDENT  LIST  OF  APPARATUS. 

Several  glass  slips  3X1  inch,  and  more  circle  glass  covers, 
thin  and  |-  inch  diameter. 

One  scalpel. 

One  pair  forceps,  fine  points. 

Two  dissecting  needles  (may  be  made  by  thrusting  with  aid  of 
pincers  a  sewing  needle  in  the  end  of  a  small  soft  pine  stick). 

Lead-pencils,  one  medium  and  one  hard. 

Note  paper;  a  good  paper,  about  octavo  size,  smooth,  unruled, 
with  two  perforations  on  one  side  for  binding.  Several  manila 
covers  or  folders  to  contain  the  paper,  perforated  also.  Enough 
covers  should  be  provided  so  that  notes  and  illustrations  on  dif- 
ferent subjects  can  be  kept  separate. 

REFERENCE    BOOKS. 

The  following  books  are  suggested  as  suitable  ones  to  have  on 
the  reference  shelves,  largely  for  the  use  of  the  teacher,  but  sev- 


REFERENCE   BOOKS. 


723 


eral  of  them  can  with  profit  be  consulted  by  the  students  also. 
There  are  a  number  of  other  useful  reference  books  in  Ger- 
man and  French,  and  also  a  number  of  journals,  which  might  be 
possessed  by  the  more  fortunate  institutions,  but  which  are  too 
expensive  for  general  use,  and  they  are  not  listed  here. 

Kerner  and  Oliver,  Natural  History  of  Plants.  Blackie  &  Son, 
London,  1895.  Henry  Holt  &  Co.,  New  York,  1895. 

Strasburger,  Noll,  Schenck  &  Schimper,  A  Text  Book  of  Bot- 
any, translated  by  Porter.  The  Macmillan  Co.,  New  York, 
1898. 

Vines,  Student's  Text  Book  of  Botany.  The  Macmillan  Co., 
New  York,  1895. 

Atkinson,  The  Biology  of  Ferns.  The  Macmillan  Co.,  New 
York,  1894. 

MacDougal,    Experimental    Plant    Physiology.       Longmans, 
1  Green  &  Co.,  New  York. 

Spalding,  Introduction  to  Botany.  D.  C.  Heath  &  Co.,  Bos- 
ton, 1895. 

Bessey,  Essentials  of  Botany.  Henry  Holt  &  Co.,  New 
York. 

Goebel,  Outlines  of  Classification  and  Special  Morphology  of 
Plants.  Oxford,  Clarenden  Press,  1887. 

Warming  &  Potter,  Hand  Book  of  Systematic  Botany.  Mac- 
millan &Co.,  New  York,  1895. 

DeBary,  Comparative  Morphology  and  Biology  of  the  Fungi, 
Mycetozoa,  and  Bacteria.  Oxford,  Clarenden  Press,  1887. 

Underwood,  Our  Native  Ferns  and  their  Allies.  Henry  Holt 
&  Co.,  New  York. 

Bailey,  Lessons  in  Plants.  Macmillan  &  Co.,  New  York, 
1898. 

Gray,  Lessons  and  Manual  of  Botany.  American  Book  Co., 
New  York. 

Miiller,  The  Fertilization  of  Flowers.  Macmillan  &  Co.,  New 
York. 

Darwin,  Insectivorous  Plants.  D.  Appleton  &  Co.,  New 
York. 


724  APPENDIX. 

Darwin,  The  Power  of  Movement  in  Plants.  D.  Appleton  & 
Co.,  New  York. 

Darwin,  Cross  and  Self  Fertilization  in  the  Vegetable  King- 
dom. D.  Appleton  &  Co.,  New  York. 

Warming,  Oekologische  Pflanzengeographie.  Gebriider  Born- 
trager,  Berlin. 

Campbell,  A  University  Text-book  of  Botany.  The  Macmil- 
lan  Co.,  New  York,  1902. 

Schimper,  Plant  Geography  on  a  Physiological  Basis.  Eng- 
lish translation,  W.  R.  Fisher,  revised  and  edited  by  P.  Groom 
and  I.  B.  Balfour,  Oxford,  1903. 

Papers  by  Macmillan  and  others  in  the  Bulletin  of  the  Torrey 
Botanical  Club,  and  Minn.  Bot.  Studies,  by  Shaler,  in  the  6th, 
loth,  and  i2th  Ann.  Repts.  of  the  United  States  Geological 
Survey;  by  Ganong,  Cowles,  and  others  in  the  Botanical  Gazette. 

In  a  pamphlet  of  67  pages,  being  an  outline  of  a  course  of 
lectures  on  the  relation  of  plants  to  environment  by  Geo.  F. 
Atkinson,  there  are  nine  pages  devoted  to  bibliography. 

Where  materials  cannot  be  readily  collected  in  the  region  for 
class  use,  they  can  often  be  purchased  of  supply  companies. 

The  Plant  Study  Co.  and  the  Cambridge  Botanical  Supply 
Co.,  of  Cambridge,  Mass.,  supply  plant  material  of  several 
groups  for  study,  as  well  as  apparatus  and  paper. 

The  St.  Louis  Biological  Laboratory  also  supplies  plants,  and 
especially  prepared  slides  of  microscopic  preparations,  as  well  as 
lantern  slides. 


INDEX. 


Absorption,  13,  22-28 

Acclimatization,  469 

Aceracese,  685,  707 

Acer  saccharinum,  685 

Acorn,  451 

Acorus  calamus,  662,  703 

Adansonia,  534 

/Ecidiomycetes,  218 

j^Ecidiospore,  189 

^sculus  hippocastanum,  686,  707 

Agaricaceae,  199,  219 

Agaricus  arvensis,  206 

Agaricus  campestris,  200-207 

Agave,  560 

Agropyron  dasystachyum,  592,  594 

Agropyron  pseudorepens,  561,  563 

Agropyron  tenerum,  590 

Agrostis  hiemalis,  602 

Akene,  451 

Albumen,  98 

Albuminous,  98,  108 

Alder,  704 

Algae,  136-176,  589,  653 

Algae,  absorption  by,  22 

Alismaceae,  702 

Alkaline  basins,  618 

Almond  family,  680 

Alpine  formation,  516,  526 

Alpine  plant  societies,  582-585 

Alum-root,  602 

Amanita  phalloides,  207,  208 

Amaranth,  705 

Amaryllidaceae,  703 

Aments,  429 

American  mistletoe,  705 

Ammophila  arenaria,  592,  599 

Ammophila  arundinacea,  594 

Ampelopsis,  708 

Ancylistales,  215 

Andreales,  249 

Andrcecium,  319,  419 


Andromeda  polifolia,  609 
Andropogon  furcatus,  559,  561 
Andropogon  scoparius,  559.  561 
Anemophilous,  435 
Angiosperms,  morphology    )f,   318- 

348 
Angiosperms,  representative  families, 

648-701 

Antennaria  campestris,  562 
Antheridiophore,  227 
Antheridium,  144, 149, 155,  176,  223, 

228,  240,  24^,,  246,  266.  287,  433 
Anthesis,  429 

Anthoceros,  240,  241 

Anthocerotales,  242 

Anthocerotes,  242 

Apogamy,  346 

Apogeotropic       (ap"o-ge"o-trop'ic), 

126 
Apogeotropism     (ap"o-ge-ot'n>- 

pism),  126 
Apple,  456,  68 1,  706 
Apple  family,  680,  706 
Aquatic  formations,  521,  526 
Aquatic  plant  societies,  620-629 
Araceae,  662,  703 
Archegonia     (ar-che-go'ni-a),     225. 

229,  233,  241,  244-2*6,  267,  288, 
291,  307-308 

Archegoniophore,  223 

Archegonium,  433 

Archesporium      (ar"che-spo/ri-utn), 

235 

Archidiales,  249 

Arctic  formation,  516,  526,  576-582 
Arenaria  stricta,  602 
Aril,  457 

Arisaema,  662-666,  703 
Arisaema  triphyllum,  442,  443 
Aristolochiales,  705 
Arrow  leaf,  625,  626,  702 

725 


726 


INDEX. 


Artemisia  canadensis,  590,  591 
Artemisia  caudata,  590,  591 
Artemisia  spinescens,  572 
Artemisia  tridentata,  559,  570 
Arum  family,  662,  703 
Arundinaria,  538,  617 
Asclepias,  710 
Asclepias  cornuti,  462 
Ascomycetes  (~s-co-my-ce'tes),  195- 

198,  216-218 

Ascophyllum  nodosum,  622,  629 
Ascus,  190,  213 
Ash  of  plants,  79,  80 
Ash  tree,  710 

Aspidium  acrostichoides,  253,  257 
Assimilation,  67,  109"  . 

Aster,  712 

Aster  novae-angliae,  697-700 
Atoll  moor,  611-615 
Atriplex,  563,  572,  705 
Atriplex  canescens,  570 
Atriplex  confertifolia,  572 
Auriculariales,  218 
Austral  forests,  535 
Autotrophic  plants,  8g_ 
Autumn  colors,  535 
Autumnal  flora,  562 
Azalea,  709 
Azolla,  296,  627 

Bacteria,  164,  165,  623,  624,  626 

Bacteria,  nitrite  and  nitrate,  83 

Bacteriales,  164,  165 

Bacteroid,  93 

Bad  Lands,  562 

Bald  cypress,  537,  538 

Bangiales,  175 

Banyan  tree,  533 

Basidiomycetes    (Ba-sid"i-o-my-ce' 

tes),  199-208,  218 
Basidium,  201,  213 
Bassweed,  625,  626 
Bast,  50-52 

Batrac^ospermum,  171-173,  175 
Bazzania,  25 
Beard  grasses,  559,  561 
Bedstraws,  711 
Beechnut,  452 

Beet,  osmose  in,  15,  16,  17,  18 
Begonia,  407 
Bellflower,  711 
Benthos,  621  • 

Berry,  454,  455,  456 
Betulaceae,  704 


Bicuculla,  706 

Bidens,  458 

Bignonia,  711 

Big  trees,  538-541 

Bilberries,  709 

Biothermal  lines,  501,  503 

Biotic  factors,  479,  509 

Birch,  704 

Bird's-nest  fungi,  220 

Blackberry,  454 

Black  fungi,  198 

Bladderwort,  610,  711 

Blasia,  164,  236 

Bloodroot,  706 

"Blowouts,"  599,  561 

Bluets,  436,  437,  602,  711 

Boletus,  209 

Boletus  edulis,  209 

Boraginacese,  710 

Boreal  forests,  534 

Botrychium,  295 

Botryo^iaceae,  162 

Botrydium  granulatum,  146,  162 

Bouteloua  oligostachya,  559,  562 

Broom  sedge,  559 

Brown  algae,  628;  uses  of,  170 

Bryales,  349 

Bryophyta  (Bry-oph'y-ta),  653 

Bud  sage,  572 

Buds,  winter  condition  of,  374-377 

Buckeye  family,  686,  707 

Buckthorn,  708 

Buckwheat,  705 

Buffalo-grass,  559 

Bug  seed,  563,  705 

Bulb,  372 

Bulbilis  dactyloides,  559 

Bulrushes,  606,  625 

Bunch-grasses,  559,  561 

Burr-grass,  590 

"Bush,"  516 

Buttercup,  676 

Butternut,  452,  670,  704 

Butterwort,  610 

Buttes,  562,  563 

Buttonbush,  711 

Buttonwood,  706 

Cacti,  395, 559, 560, 566, 570-573,  708 
Cakile  edentula,  590 
Cakile  fusiformis,  590 
Calamagrostis  longifolia,  594 
Calamovilfa  brevipilis,  592 
Calla  palustris,  662 


INDEX. 


727 


Callithamniom,  173 
Calluna  vulgaris,  616 
Calyptrogen,  361 
Cambium,  50,  52,  358,^363 
Campanula  rotundifolia,  442,  444, 

601,  711 

Campanulales,  697,  711 
Cane  swamp,  617 
Canna,  445-449,  703 
Capsella  bursa-pastoris,  676,  706 
Capsule,  453 

Carbohydrate,  71,  75,  80,  90 
Carbon  dioxide,  62-67,  110-113 
Cardinal  flower,  711 
Cardinal    temperature   points,   468, 

469 

Carex,  607 
Carex  filiformis,  611 
Carex  laxi  flora,  66 1 
Carex  lupulina,  660 
Carpogonium,  172,  176 
Caryophyllaceae,  705  • 

Caryopsis,  451 
Cassia  marilandica,  402 
Cassiope,  395,  580 
Cassiope  tetragona,  610 
Castalia  odorata,  627,  705 
Castor-oil  plant,  707 
Catarpa,  711          T 
Catkin,  428 
Catnip,  695 
Cattail-flag,  702 
Caulerpa,  628 
Caulidium,  371 
Cedar  apples,  194 
Cedar  of  Lebanon,  406 
Cell,  3;  artificial,  20 
Cell  sap,  3,  40 

Cerichrus  macrocephalus,  590 
Ceratopteris  thalictroides,  296 
Cereus,  560 
Chaetophora,  151,  162 
Chaetophoraceae,  162 
Chaparral,  530,  531 
Chara,  176,  625,  626 
Charales,  176 

Chemical  condition  of  soil,  473 
Chemosynthetic  assimilation,  109 
Chenopodiales,  705 
Chenopods,  563,  564,  705 
Chestnut,  45  2>  7°4 
Chestnut  trees,  534 
Chicory  family,  700,  711 
Chlamydomonas,  159,  160 


Chlamydospores,  180 
Chloral  hydrate,  65,  87 
Chlorophyceas,  158 
Chlorophyll,  2,  67,  72 
Chloroplast,  68,  69,  71 
Christmas  fern,  251-253 
Chromoplast,  71 
Chromosomes,  342-345 
Chroococcaceae,  163 
Chrysanthemum,  712 
Chytridiales,  215 
Cichoriaceae,  700,  711 
Cichorium  intybus,  711 
Cladophora,  626,  627 
Clavaria  botrytes,  212 
Clavariaceae,  210,  219 
Claytonia  virginica,  705 
Cleistogamous,  435 
Clematis  virginiana,  462,  463,  674 

675,  706 

Climatic  factors,  477 
Climatic  formations,  514-518 
Climatic  pressures,  510,  512 
Clostridium  pasteurianum,  93 
Clover,  707 
Club  mosses,  284,  289 
Cnicus  pitcheri,  591 
Coccogonales,  163 
Cocklebur,  711 
Cold  wastes,  516 
Coleochaetaceae,  162 
Coleochaete,  153-156,  226,  626 
Collenchyma,  356,  363 
Comandra,  705 
Compass  plants,  409 
Composites,  697,  712 
Comptonia  asplenifolia,  704 
Cone  fruit,  456 
Confervoideae,  162 
Coniferae,  316 

Conjugation,  137,  141,  160,  162,  i7g 
Convallariaceae,  703 
Cooperia,  703 
Cordyceps,  218 
Coreopsis,  712 
Corispermum    hyssopifolium,    536. 

590 

Cork,  357,  363 
Corm,  373 

Cornus  stolonifera,  594 
Cortex,  50 
CorymV^  427 
Cotton-grass,  617 
Cottonwood,  592 


728 


INDEX. 


Cotyledon,  99-101 

Cranberry,  709 

Crataegus,  707 

Crowfoot  family,  673,  706 

Cruciferae,  652,  676,  706 

Cryptonemiales,  175 

Cucurbitaceae,  711 

Culture  formations,  521,  526 

Cultures,  water,  28,  29 

Cup  fungi,  199 

Cupuliferae,  669,  704 

Cuscuta,  83,  710 

Cushion  type  of  vegetation,  584-585 

Cuticle,  43 

Cyanophycese,  163,  589,  622,  624 

Cyatheaceae,  295 

Cycadales,  316 

Cycas,  311,  312,  457 

Cyclosis,  9,  10 

Cyclosporales,  171 

Cyme,  430,  432 

Cyperaceae,  659,  702 

Cyperus,  607 

Cypress,  534,  537,  49* 

Cypripedium,  443,  447,  666,  703 

Cystocarp,  174 

Cystopteris  bulbifera,  260 

Cystopus,  215 

Cytase,  92,  108 

Cytisus,  445 

Cytoplasm  (cy'to-plasm),  5 

Dacryomycetales,  219 
Dahlia,  108 
Dandelion,  700,  711 
Dasiphora  fruticosa,  619,  706 
Daucus  carota,  691,  692,  708 
Death's  valley,  568 
Dehiscence,  453 
Dentaria,  322-324,  676 
Dentaria  diphylla,  652,  653,  706 
Dermatogen,  359 
Desert  formation,  517,  526 
Desert  plant  societies,  565-575 
Desmodium,  458 
Desmodium  gyrans,  399 
Diadelphous  (di"a-del'phous),  425 
Diageotropism  (di//a-ge-ot'ro-pism) , 

126 
Diaheliotropic      (di^a-he^li-o-trop'- 

ic),   127 
Diaheliotropism      (di"a-he"li-ot'ro- 

pism),  127 
Diastase,  77,  78,  108,  116 


Diatoms,  166,  622,  626 
Dichogamous  (di-chog'a-mous),  437, 

442 

Dicentra,  706 

Dicotyledons,  651,  652,  667-701,  704 
Dictyophora,  219 
Diffusion,  13-20 
Digestion,  107,  108,  109 
Dimorphism  of  ferns,  273-280 
Dioecious,  435 

Dionaea  muscipula,  133,  611 
Dipodascus,  216 
DipSacus,  711 
Discomycetes,  217 
Distichlis,  563 
Distribution,  497 
Dodder,  83,  84,  710 
Dogwood,  708,  709 
Dondia  linearis,  590 
Dothidiales,  218 
Downy  mildews,  185 
Drosera,  706 
Drosera  rotundifolia,  133 
Drupaceae,  680,  707 
Drupe,  454 
Duck  meat,  627 
Duckweeds,  26,  28,  627,  665 
Dudresnaya,  175 
Dune-forming  plants,  593,  594 
Dunes,  kinds  of,  592,  593;  methods 

of  checking,  598,  599;  vegetation 

of,  592-599 
Dysphotic  region,  621 

Eatonia  obtusata,  559 

Ebenales,  710 

Ecological  factors,  464,  465 

Ecology    (sometimes  written  cetol 

ogy),  464 
Ectocarpus,  167 

Edaphic  formations,  518,  526,  560 
Elaphomyces,  217,  218 
Elder,  711 

Elm  family,  672,  704 
Elodea,  61-63 

Elymus  canadensis,  561,  590,  594 
Embryo  of  ferns,  269-272 
Embryo  sac,  326-328 
Empusa,  215 
Endocarp,  450 
Endomyces,  216 
Endosperm,  103,  105,  107,  306,  309-, 

nucleus,  327,  329-334 
Enteromorpha,  628 


INDEX. 


729 


Entomophthorales,  215 

Enzyme,  92,  38,  116,  117 

Epidermal'system,  358 

Epidermis,  358,  359,  363 

Epigaea  repens,  709 

Epigynous,  425 

Epilobium,  708 

Epinastic  (ep-i-nas'tic),  129 

Epinasty  (ep'i-nas-ty),  129 

Epipactis,  444,  447,  665 

Epiphegus,  84 

Epiphytes,  416,  544,  621 

Equisetales,  296 

Equisetineae,  296 

Equisetum,  280-283 

Ericaceae,  709 

Ericales,  709 

Erythronium,  649,  654,  703 

Etiolated  plants  (e/ti-o-la"ted),  68 

Euasgomycetes,  217 

Eubasidiomycetes,  219 

Eupatorium,  403,  712 

Euphorbia  polygonifolia,  590,  592 

Euphorbiaceae,  707 

Eurotia  lanata,  572 

Eurotium  oryzae,  78 

Evening  primrose  family,  689-708 

Exalbuminous,  108 

Exoascus,  217 

Exobasidiales,  ,219 

Exocarp,  450 

Facies,  525 

Fagales,  669,  704 

Fehling's  solution,  75,  76,  712 

Ferment,  98,  108,  116 

Fern,  "walking,"  508,  509 

Ferns,  251-279,  292,  457;  classifica- 
tion of,  295;  of  rocky,  places,  601 

Fertilization,  307,  308,  328,  329,  140, 
145,  169,  172,  174,  197,  421 

Fibrovascular  bundles,  49-54 

Fig  wort  family,  696,  710 

Filicales,  295 

Filicineae,  295 

Fittonia,  404 

Flagellates,  83,  165 

Flax,  707 

Flora,  497 

Flower  cluster,  419 

Flower,  form  of,  422;  parts  of,  419; 
union  of  parts,  424 

Flowers,  arrangements  of,  426;  kinds 
of,  421 


Follicle,  453 

Fontinalis,  626,  627 

Forest,  516;  enemies  of,  552;  forma- 
tions, 560;  longevity  of,  531;  pro- 
tection, 551;  regeneration,  548- 
552;  societies,  529~555;  structure 

of>  53 1 

Forests,  relation  to  rainfall,  546 

Formations,  aquatic,  625-625;  study 
of,  630-647 

Fragaria  vesca,  680 

Fraxinus  americana,  602 

Freezing,  470 

Fresh-water  societies,  624 

Frond,  352 

Fruit,  450-457,  507;  Parts  of,  450 

Frullania,  25,  236 

Fucus,  i68jj:7o,  622 

Fungi,  653;  absorption  by,  22;  classi- 
fication of,  213-222;  nutrition  of, 
86-90;  respiration  in,  115 

Gametangium      (gam"et-an'gi-um), 

140 

Gamete  (gam'ete),  138,  139 
Gametophore  (gam'et-o-phore),  230, 

248 
Gametophyte  (gam'et-o-phyte),  225, 

226,  244,  245,  250,  262,  270,  283, 

292,  294,  305,  314,  317,  336-339, 

340-348,  434 
Gamopetalous     (gam"o-pet'a-lous) , 

424 
Gamosepalous     (gam-o-sep'a-lous), 

424 

Gas  in  plants,  60-64 
Gasteromycetes,  219 
Gemmae,  179,  235 
General  formations,  526 
Gentian,  710 
Geotropism     (ge-ot'ro-pism),     125- 

127,  410 

Geraniaceae,  677,  707 
Geraniales,  676,  707 
Geranium  family,  677,  707 
Germ,  459 
Gigartinales,  175 
Gingko,  313-315,  457 
Gingkoales,  316 
Ginseng,  708 

Glaciers,  influence  of,  510-511 
Glasswort,  563,  705 
Gleicheniaceae,  295 
Glucose,  108.     See  sugar. 


730 


INDEX. 


Gnetales,  316 

Gonidia,  118,  143,  172,  174,  178-184 

Gonidiangium      (go"nid-an'gi-um), 

178 

Gonidium,  213 
Gooseberry,  706 
Goose  foot  family,  705 
Gracilaria,  173,  174,  175 
Grama  grass,  559,  562 
Graminales,  657,  702 
Graminese,  657,  702 
Grape,  708 

Grass  family,  657,  702 
Grasses,  607,  625 

Grassland  formation,  517,  526,  556 
Grease  woods,  564 
Green  algae,  158,  628 
Ground  covers,  471 
Growth,  118-124,  380 
Gulf  weed,  170 

Gymnosperms,  311,  456,  653 
Gymnosporangium,  194 
Gynoecium,  320,  419,  451,  452 
Gyrocephalus,  219 

Halophytes,  484,  563,  619,  621 
Halophytic  structures,  495 
Harebell,  60 1 
Harpochytrium,  214,  215 

Haustorium,  87,  88 

Hawk  weed,  700,  711 

Hawthorn,  707 

Hazelnut,  452,  704 

Head,  428 

Heart  leaf,  705 

Heat,  468,  504,  505 

Heath  family,  709 

Heath  moors,  578,  616 

Heather,  616 

Heliotrope,  710 

Heliotropism          (he-li-ot'ro-pism), 

127-131,  133,  397 
Helvellales,  217 
Hemiascomycetes,  216 
Hemibasidiomycetes,  218 
Hepaticae,  242 
Heteranthera,  627 
Heterospory  (het"er-os'po-ry),  434 
Heterothallic,  180 
Heterotrophic  plants,  85 
Heuchera  americana,  602 
Hickory,  704 
Hickory  nut,  452 


Hieraceum  venosum,  700 
Hilum,  101,  102 
Hippocastanaceae,  686,  707 
Holdfasts,  418 
Hollyhock,  708 
Homothallic,  180 
Honeysuckle,  711 
Hormogonales,  163 
Horse-chestnut,  686,  707 
Horsetails,  280-283 
Hot  springs,  vegetation  of,  624 
Houstonia  caerulea,  437;    purpurea 

601;  Houstonia,  711 
Huckleberry,  709 
Humus  saprophytes,  85,  91,  709 
Hybridization,  338 
Hydnaceae,  210,  219 
Hydnum  coralloides,  210 
Hydnum  repandum,  211 
Hydrocarbon,  75 
Hydrodictyaceae,  161 
Hydrodynamic  forces,  467 
Hydrophytes,  484,  620,  621 
Hydrophytic  structures,  490 
Hydropterales,  295 
Hydrotropism         (hy-drot'ro-pism), 

133,  134,  412 
Hygrophytes,  485 
Hymeniales,  219 
Hymenogastrales,  219 
Hymenornycetes,  219 
Hymenomycetineae,  219 
Hymenophyllaceaa,  295 
Hypericum,  708 
Hypocotyl  (hy'po-co"tyl),  101 
Hypocreales,  217 
Hypogenous,  425 
Hyponasric  (hy-po-nas'tic),  129 
Hyponasty  (hy'po-nas-ty),  129 
Hysteriales,  217 

Impatiens,  707 

Impatiens  fulva,  460 

Indian-grass,  559 

Indian-pipe,  709 

Indian-turnip,  662,  703 

Individual  formations,  522-524,  526 

Indusium,  252 

Inflorescence,  426 

Insectivorous  plants,  133,  610,  611, 

706 

Integument,  304 

Intramolecular  respiration,  113,  114 
^Inulase,  108 


INDEX. 


731 


Inulin,  108,  417 

Iodine,  65 

Ipomoea,  710 

Ipomoea  acetosaefolia,  590 

Ipomoea  pes-caprae,  590,  592 

Iridaceae,  703 

Iris,  703 

Irritability,  125-135 

Isoetales,  296 

Isoetes,  289-291,  292,  627 

Isoetineae,  296 

Iva  imbricata,  599 

Ivy,  708 

Jack-in-the-pulpit,  373 
Jewelweed,  707 
Juglandales,  704 
June-berry,  707 
Jungermanniales,  242 

Kalmia  latifolia,  444 
Karyokinesis,  341-344 
Kelps,  1 68 
Kingdom,  653 
Kochia  americana,  572 
Koehleria  cristata,  559 

Labiatae,  423,  694,  710 

Laboulbeniales,  218 

Labrador  tea,  609,  709 

Lactuca  canadensis,  460 

Lactuca  scariola,  409,  460,  461 

Lagenidium,  214,  215 

Laminaria,  168,  169,  628 

Lamium,  424,  694,  710 

Larch,  367 

Lathyrus  maritimus,  592    * 

Laurel,  709 

Layers,  525 

Leaf  patterns,  404 

Leather  leaf,  609 

Leathesia  difformis,  168 

Leaves,  form  and  arrangement,  383- 
391;  function  of,  387;  protective 
modifications  of,  392;  protective 
positions,  395;  reduction  of  sur- 
face, 394;  relation  to  light,  397; 
structure  of,  40-43,  131,  391,  393 

Legumes,  92,  93,  453  ^ 

Leguminosae  (=Papilionaceae),  396, 

399 

Leitneria  floridana,  704 
Leitneriales,  704 


Lemanea,  171,  173,  175,  492,  623, 
626,  627 

Lemna,  418,  627 

Lemna  trisulca,  26,  27 

Lenticel,  357,  358 

Lepiota  naucina,  208 

Lettuce,  711 

Leucoplast,  71 

Liana,  545 

Lichen  tundra,  579 

Lichens,  86,  93-95,  220,  221,  578; 
formations  on  rocks,  600-603 

Life  areas,  500-504 

Life  regions,  500-504 

Life  zones,  500-504,  641-647 

Light,  467 

Light,  regions  of,  in  water,  621 

Liliaceae,  650-652,  654,  703 

Liliales,  651,  652,  654,  703 

Lilium,  650,  703 

Limnetic  plant  societies,  624-627 

Linaria  vulgaris,  696,  711 

Linden,  708 

Linum  vulgaris,  707 

Lipase,'  108 

Liquidambar,  706 

Liriodendron,  706 

Lithophytes,  621., 

Live-forever,  394 

Liverworts,  222-239,  653;  absorp- 
tion by,  23-25;  classification  of, 
242 

Lobelia,  711 

Lupinus  perennis,  3553 

LycoperdaJPs,  220 

Lycopodiaceae,  296 

Lycopodiales,  296 

Lycopodiineae,  296 

Lycopodium,  2§4~286 

Macrophytes,  622 
Macrosporangium,  94,  302,  304,  311, 

312,  321 

Macrospore,  287,  290,  326-328,  434 
Magnolia,  705,  706 
Mallow  family,  708 
Malvales,  708 

Mangrove  swamps,  538,  618 
Maple  family,  685,  707 
Marchantia,  24,  226-236 
Marchantiales,  242 
Marine  plant  societies,  627-629 
Maritime  ruppia,  618 
Marl  ponds,  619,  624 


732 


INDEX. 


Marram  grass,  592,  599 
Marratiales,  295 
Marsilia,  370,  625,  627 
Marsiliaceae,  296 
Marshes,  alkaline,  563 
Matoniaceae,  295 
Meadow  swamps,  607 
Meadows,  561,  628 
Medicago  denticulata,  92 
Medulla,  50 

Members  of  the  flower,  335 
Members  of  the  plant,  349-353 
Meristem,  359 
Mesocarp,  450 
Mesophytes,  483,  485,  493 
Mesophytic  structures,  492 
Mesquite,  560 
Microphytes,  621 
Microsporangia,  294,  299 
Microspore,  287,  290,  299,  312,  435 
Microsporophylls,  299,  320,  420 
Migration,  barriers  to,   513;    causes 

of,    506,  509-513;   laws   of,  497; 

lines  of,  500 
Milkweed,  462 
Milkweed  family,  710 
Mimosa,  132,  396 
Mimulus,  710 
Mint  family,  694,  710 
Mistletoe,  84,  705 
Mitchella,  711 
Mixotrophic  plants,  85 
Mnium,  243-246 
Molds,  nutrition  of,  86-90 
Molds,  water,  181 
Monadelphous,  424 
Monoblepharidales,  215 
Monoblepharis,  215 
Monocotyledons,  651-666,  702 
Monoecious,  435 
Monotropa  uniflora,  709 
Morchella,  198,  199 
Morel,  198,  199 
Morning-glories,  590,  710 
Mosaics,  405 
Moss  tundra,  578 
Mosses,    243-248,   457,    584,    653; 

absorption  by,  25;  classification  of, 

248 

Mucor,  6, 7, 15, 118, 119, 177-180,215 
Mucorales,  215 
Mud  swamp,  606 
Mulberry,  704 
Mullein,  366,  394,  710 


Mushrooms,  199-208,  552-555 
Muskeag,  607 
Mustard  family,  676,  706 
Mutation,  338 
Mutualism,  95 
Mycelium,  6,  86-90 
Mycetozoa,  213,  214 
Mycorhiza,  86,  91,  92,  217 
Myosotis,  710 
Myrica  cerifera,  704 
Myrica  gale,  704 
Myricales,  704 
Myriophyllum,  403 
Myrtales,  689,  708 
Myxobacteriales,  165 
Myxomycetes,  83,  213,  214 

Naiadaceae,  702 

Naiadales,  702 

Naias,  627,  702 

Nemalion,  171,  172,  175 

Nemalionales,  175 

Nepeta  cataria,  695 

Nettle,  704 

Nicotiana,  710 

Nidulariales,  220 

Nitella,  8,  9,  176 

Nitrobacter,  83 

Nitrogen,  92,  93 

Nitromonas,  83 

Nostoc,  589 

Nostocaceae,  164 

Nucellus,  304 

Nucleus,  3, 4;  morphology  of,  340-345 

Nuphar  advena,  627,  705 

Nutation,  123,  124 

Nymphsea  odorata,  627,  705 

Oak,  669-671,  704 
Oak  family,  669,  704 
Oases,  warm,  581 
CEdogoniaceae,  162 
CEdogonium,  147-151,  350,  626 
(Enothera  biennis,  592,  690,  708 
(Enothera  gigas,  338 
CEnothera  lamarkiana,  338 
Olpidium,  214,  215 
Onagra  biennis,  708 
Onagraceae,  689,  708 
Onoclea  sensibilis,  254,  273-278 
Oogonium,  144,  150,  155 
Oomycetes,  214,  215 
Ophioglossales,  295 
Ophioglossum,  295 


INDEX. 


733 


Opuntia,  559 
Opuntiales,  708 
Orchidaceae,  665,  703 
Orchidales,  665,  703 
Orchids,  442 
Oscillatoria,  589 
Oscillatoriaceae,  163 
Osmosis,  13-20 
Osmundacese,  295 
Ostrich  fern,  279 
Ovule,  302,  321,  334,  421 
Oxalis,  707 
Oxycoccus,  709 
Oxydendrum  arboreum,  709 
Oxygen,  63,  110-113 

Pacific  forests,  538 

Palisade  cells,  41,  43 

Palmaceae,  702 

Palmales,  702 

Palms,  408 

Palustrine  forest,  537 

Pandanales,  702 

Panicum  scribnerianum,  559 

Pandanus,  702 

Pandorina,  160,  350 

Panicle,  427 

Panicum  amarum,  599 

Panicum  halophilum,  599 

Panicum  repens,  599 

Papaverales,  652,  676,  706 

Papilionacete,  423,  682,  707 

Parasites,  83,  84,  86,  527,  628 

Parasitic  fungi,  nutrition  of,  86-90 

Parenchyma,  50,  356,  363 

Parietales,  687,  708 

Parkeriaceae,  296 

Parmelia,  96 

Parmelia  contigua,  602 

Parsley  family,  692;  ^carrot  family, 

Parthenogenesis,  184  [708 

Partridge  berry,  711 

Pea,  683,  707 

Pea  family,  682,  707 

Pear,  456,  682 

Peat  moors,  578,  607 

Peat  moss,  608 

Pediastrum,  161 

Pelagic  plant  societies,  627-629 

Pellia,  164 

Pellonia,  405 

Peltigera,  94,  95 

Pepo,  456 

Pericycle,  360 


Peridineae,  166 

Perigynous,  425 

Perisperm,  331,  332 

Perisporiales,  217 

Peronospora,  183,  215 

Peronosporales,  215 

Persimmon,  710 

Peucedanum  foeniculaceum,  562 

Peucephyllum  schattii,  571 

Pezizales,  217 

Phacidiales,  217 

Phaeophyceae,  167 

Phaeosporales,  171 

Phallales,  219,. 

Phloem,  50-52,  360,  361,  363 

Phlox  family,  710 

Phoradendron  flavescens,  84,  705 

Photic  region,  621,  628 

Photosynthesis,  67,  68,  70,  117,  622 

Phy  corny  cetes     ( Phy"co-my-ce'tes) , 

214,  215 
Phyllidium,  371 
Phylloclades,  373,  395 
Phyllotaxy,  375,  384 
Physical  condition  of  soil,  475,  476 
Physical  factors,  465-476 
Physiography,  479 
Phytolaccaceae,  705 
Phytomyxa  leguminosarum,  92 
Phytophthora,  182,  184,  215 
Pickerel  weed,  626,  703 
Pilularia,  296,  627 
Pinales,  216,  653 
Pine,  white,  297-310 
Pinguicula  vulgaris,  610 
Pinus  divaricatus,  602 
Pinus  scopularum,  560 
Pinus  strobus,  602,  653 
Piperales,  704 
Pisum  sativum,  683 
Pitcher-plant,  610,  706 
Pith,  50 

Plains'  formations,  559 
Plankton,  621 
Plant-food,  sources  of,  81 
Plant-formations,  5 1 5-5  28 
Plant-substance,  analysis  of,  79,  80 
Plantaginales,  711 
Plantago,  711 

Plasmolysis  (plas-mol'y-sis),  19 
Plasmopara,vi83,  215 
Plectascales,  217 
Plectobasidiales,  220 
Pleurococcaceae,  161 


734 


INDEX. 


Pleurococcus,  161 

Plum  family,  680,  707 

Plumule,  99 

Podostemon,  626,  627,  706 

Poison-hemlock,  708 

Poison-ivy,  707 

Poison-oak,  707 

Poisonous  mushrooms,  207,  208 

Poison-sumac,  707 

Pokeweed,  705 

Polemoneales,  694,  710 

Pollen-grain,  299,  305 

Pollination,  303,  304,  420,  430,  433- 

449,  479 
Pollinium,  420 
Polygonales,  705 
Polygonum,  705 
Polypodiacese,  296 
Polyporacese,  209,  219 
Polyporus,  209,  210 
Polyporus  mollis,  90 
Polyporus  sulphureus,  209 
Pomaceae,  680,  706 
Pond-lilies,  625,  626 
Pondweeds,  626,  702 
Poppy,  705 

Populus  balsamifera,  592,  594 
Populus  mono lif era,  592,  594 
Populus  tremuloides,  602 
Porella,  237 
Portulaca,  705 
Postelsia,  492. 
Potamogeton,  702 
Potamogeton  natans,  625,  627 
Potato,  710 

Potentilla  fruticosa,  619 
Powdery  mildews,  195-198,  217 
Prairie  formations,  557 
Prairie  societies,  556-560 
Primrose,  708,  710 
Primula,  438 
Primulales,  710 
Principal  formations,  522,  526 
Procarp,  172,  174,  175 
Progeotropism   (pro"ge-ot'ro-pism) , 

126 

Promycelium  (pn/'my-ce'li-um),  192 
Prosopis  juliflora,  560 
Protection  to  plants,  471-473 
Proterandrous,  441,  442 
Proterandry,  444 
Proterogenous,  441,  442 
Proterogeny,  440 
Prothallium,  265,  287,  288,  291,  292, 


304,  305,3H,  325,  328,  335,  433, 

434 

Protoascales,  216 
Protoascomycetes,  216 
Protobasidiomycetes,  218 
Protococcoideae,  158,  621 
Protodiscales,  217 
Protomyces,  216 
Protonema      (pro"to-ne'ma),      248, 

264 
Protoplasm,     1-12,      42-43,      342; 

movement  of,  7-11 
Prunus  pumil^,  590,  594 
Prunus  virgiruana,  68 1 
Psilotaceae,  296 

Pteridophyta  (Pter"id-oph'y-ta),  653 
Pteridophytes,  295,  434 
Pteris  cretica,  346 
Puccinia,  187 
Puff  balls,  220 
Pumpkin,  711 
Purslane,  705 
Pyrenoid,  2,  3 
Pyrenomycetes,  217 
Pyrola,  709 
Pyrus  malus,  68 1 
Pyxidium,  453 

Quercus,  669,  704 
Quercus  macrocarpa,  602 
Quillworts,  289-291,  627 
Quince,  456 

Raceme,  427 

Radicle,  99 

Ragweed,  711 

Rainfall,  477 

Rainy -season  flora,  569 

Ranales,  673,  705 

Range,  497 

Ranunculaceae,  673,  706 

Raspberry,  454,  455 

Red  algae,  171,  628,  uses  of,  175 

Red  sage,  572 

Redwood,  538 

Reed-grasses,  625,  626 

Reproduction,    137,    143,    149,    154, 

*SS,   J79>  185,  r#6 
Respiration,  it->-ii6,  117 
Rhamnales,  7    7,  708 
Rhizoids 
Rhizome,  0 

Rhizomorph  (rni1.     morph),  89 
Rhizophidium,  214,  215 


INDEX. 


735 


Rhizopus,  177-180,  215 

Rhododendron,  531 

Rhodomeniales,  175 

Rhodophyceae,  171 

Rhus  radicans,  416,  707 

Rhus  trilobata,  569 

Riccia,  23,  164,  222-226,  627 

Ricinus,  707 

Riverweed,  627,  706 
{Root,  function  of,  410-418  . 

£.oot  -hairs,  absorption  by,  19,  30,  32 
/Root-hairs,  action  on  soil,  82 
.Root  pressure,  33,  34,  45 
"Root,  structure  of,  30,  361,  362 

Root  tubercles,  92 

Roots,  kinds  of,  415  - 

Rosaceae,  679,  706 

Resales,  678,  706 

Rose  family,  679,  706 

Rosette,  405 

Rosette  plants,  580,  581,  584,  585 

Rubiales,  711 

Rudbeckia,  712 

Ruppia  maritima,  618 

Rappia  occidentalis,  563,  702 

Russian  thistle,  705 

Rusts,  187-194 

Sage-brush,  559,  560,  570 
Sahara  desert,  574 
Salicaceae,  667,  704 
Salicornia,  618 
Salicornia  herbacea,  563,  705 
Salix,  667,  704 
Salix  adenophylla,  594 
Salix  glaucophylla,  594 
Salix  polaris,  583 
Salsify,  711 
Salsola  kali,  705 
Salsola  tragus,  705 
Salt-basins,  563 
Salt-bushes,  572 
Salt-marsh,  617 
Salt-ponds,  623 
Saltwort,  590,  591,  705 
Salvinia,  627 
Salviniaceae,  296 
Samara,  451 
Sandalwood,  705 
Sand-cherry,  590,  50 
Sand-dunes,  560 
Sand-hills,.5* 


704 


SangHijy 


Sap,  rise  of,  53,  54 

Sapindales,  685,  707 

Saprolegnia,  181-184 

Saprolegniales,  215 

Saprophytes,  83-85 

Sarcobatus,  564,  572 

Sargassum,  170 

Sarracenia  purpurea,  610 

Sarraceniales,  706 

Sarsaparilla,  708 

Saxifraga  oppositifolia,  583 

Saxifrage,  706 

Scavengers,  554~555 

Schizaeaceae,  295 

Schizocarp,  451 

Schizomycetes,  164 

Schizoghyceae,  163 

Sclerenchyma,  356-357,  361,  363 

Scouring-rush,  282 

Screw-pine,  409,  702 

Scrophulariaceae,  696,  710 

Sea-beach  panicum,  599 

Sea-blite,  590 

Seacoast  marsh-elder,  599 

Sea-grass,  628 

Sea-oats,  599 

Sea-purslane,  590 

Sea-rocket,  590,  591 

Seaside-spurge,  590 

Sedge  family,  659,  702 

Sedges,  607,  625 

Seed,  dispersal  of,  458-463 

Seed  plants,  338 

Seed,  structure  of,  98,  102 

Seedlings,  97-107 

Seeds,  330-334,  507 

Selaginella,  286-288,  292 

Selaginellaceae,  296 

Semiaquatics,  625,  626 

Sensitive  fern,  273 

Sensitive  plants,  132,  396,  399 

Sequoia  sempervirens,  538,  539 

Sequoia  washingtonia=S.  gigantea, 

534,  539-541 

Sesuvium  maritimum,  590 
Sexual  organs,  144,  147 
Shadbush,  707 
Shepherd's  purse,  676,  706 
Shoot,  floral,  419,  432 
Shoots,  353-355;  types  of»  365-373; 

winter  condition  of,  374-377 
Sieve  tissue,  358,  363 
Sieve  tubes,  52,  53 
Silique,  453 


736 


INDEX. 


Silk-cotton  tree,  417 

Silver  bell,  710 

Siphoneae,  146,  162 

Skunk's  cabbage,  439-442 

Slime  molds,  83 

Smoke-tree,  707 

Snow  covers,  472 

Societies,  522,  526,  527 

Sod-formers,  558,  559,  56^ 

Solanum,  710 

Solidago,  712 

Sourwood,  709 

Spadix,  428 

Spartium,  446 

Spathyema  foetida,  438,  662,  703 

Spermagonia,  190 

Spermatophyta,  653 

Spermatophytes,  338 

Sphacelaria,  168 

Sphserella  lacustris,  158,  159 

Sphaerella  nivalis,  158,  350 

Sphaeriales,  218 

Sphagnales,  248 

Sphagnum,  164,  608-615 

Spiderwort,  u,  703 

Spike,  428 

Spinifex  squarrosus,  592 

Spirodela  polyrhiza,  27 

Spirogyra,  1-5,  13,  14,  60,  72,  136- 

140,  350,  626 
Sporangia,  178-182 
Sporangium,  253-258,  281,  290 
Spores,  225,  256-258,  263,  264,  281 
Sporobolus  asperifolius,  558 
Sporocarp,  173 
Sporogonium        (spo"ro-go'ni-um), 

224,  231,  233,  234,  237,  238,  239, 
•    241,  246,  247,  248 
Sporophyll,  274,  281,  292 
Sporophyte  (spo'ro-phyte),  225,  226, 

232,  234,   237-239,  241,  242,  250, 

261,  268,  270,  283,  292,  294,  314, 

315,  3i7>  336-339,  340-348,  434 
Spurge  family,  707 
Squash,  711 
Staminodium,  446 
Starch,    formation    of,    68,    70-74; 

changed  to  sugar,  77,  78;  translo- 

cation  of,  73;  digestion  of,  75 
Stems,  types  of,  365-373 
Stems,  woody,  structure  of,  381-382 
Stipa  spartea,  561 
Stoma     (pi.    stomata)    (sto'ma-ta), 

42-44,  46 


Strand  formations,  586 

Strawberry,  455,  680,  706 

Stress,  lines  of,  504 

Strophostyles  helvola,  591      ?<"«  " 

Succulents,  394,  395,  580 

Sugar-maple,  685 

Sugar,  test  for,  75,  76 

Sumac,  707 

Sundew,  133,  610,  706 

Sunflower,  399-401,  712 

Swamp,  606 

Swamp  societies,  620 

Sweet  gum,  706 

Symbiosis,  85,  86,  92-95,  480 

Synergids  (syn'er-gids),  327^330 

Syngencesious,  424 

Synthetic  assimilation,  67 

Tamarack  swamps,  616 

Tape-grass,  702 

Taraxacum  densleonis,  700,  711 

Taxonomy,  652 

Taxus,  534 

Teasel,  711 

Telegraph- plant,  399    . 

Teleutospore,  188 

Temperature,    134,    135,    468,   479, 

501,  507,  623,  624 
Tetrasporaceae,  161 
Tetraspores,  173,  174 
Thallophyta,  653 
Thallophytes,  352 
Thallus,  352 
Thelephoracese,  219 
Thickets,  516,  530,  704 
Thistle  family,  697,  712 
Thunderwood,  707 
Thyrsus,  427 
Tilia,  708 

Tillandsia,  491,  703 
Tissue,  tensions  of,  57-59 
Tissues,  classification  of,  363,  364; 

kinds   of,    356-359;    organization 

of>  356-302 
Toad-flax,  696,  710 
Tomato,  710 
Tradescantia,  703 
Tragopogon,  711 
Trailing  arbutus,  709 
Trailing  wild  bean,  591 
Trametes  pini,  90 
Transpiration,  35-46 
Tree  growth,  northern  limit,  576,  577 
Trees,  longevity  of,  532-534 


INDEX. 


737 


Tremellales,  218,  219 
Triadelphous,  425 
Trichodesmium  erythraeum,  622 
Trillium,  318-322,  648,  656,  703 
Trillium  grandiflorum,  520 
Tropical  forests,  541 
Tropophytes,  485,  493,  494 
Trumpet -creeper,  711 
Tuberales,  217 
Tubers,  373 
Tumbleweeds,  507 
Tundra,  516,  578 
Tupelo  gum,  538 
Turcrescence.  14,  1,5 
Turgor,  20;  restoration  of,  56,  57 
Typha,  606,  625,  702 

Ulmaceae,  672,  704 

Ulmus  americana,  672,  673,  704 

Ulothrix,  162 

Ulotrichaceae,  162 

Ulvaceae,  162 

Umbel,  428 

Umbellales,  692,  708 

Umbelliferae,  692,  708 

Uniola  paniculata,  599 

Upland  forest,  537 

Uredinales,  218 

Uredineae,  187-194,  218 

Uredospore,  189 

Uromyces  caryophyllinus,  87 

Urticales,  672,  704 

Ustilaginales,  218 

Ustilagineae,  218 

Utricularia,  610,  711 

Vaccinium,  709 
Vacuoles,  7,  8 
Valerianales,  711 
Vallisneria  spiralis,  492,  702 
Variation,  338 
Vascular  tissue,  358,  363 
Vaucheria,  142-146,  626 
Vaucheriaceae,  162 
Vegetation  elements,  497 
Vegetation  formations,  evolution  of, 

605,606 

Vegetation  forms,  525 
Vegetation  of  hot  springs,  624;   of 

rocky  places,  600-606;  of  swamps 

and  moors,  606-61 5 ;  of  the  strand, 

586-599 
Vegetation  regions  of  the  earth,  638- 

641 


Vegetation  types,  464,  465,  482,  496 

Venus'  flytrap,  133,  611 

Verbascum,  710 

Verbena,  710 

Vernal  flora,  562 

Vessels,  52,  53 

Vetch,  92,  707 

Viburnum,  711 

Vicia  sativa,  459 

Viola  cucullata,  436,  687 

Violaceas,  687,  708 

Violet  family,  687 

Virgin's-bower,  462,  463 

Vitaceae,  707 

Volvocaceae,  158 

Walnut,  452,  704 

Water,  465;  flow  of,  in  plants,  53,  54 

Water-fern,  627 

Water-lilies,  606,  625,  627,  705 

Water-plantain,  702 

White  pine,  396 

White  sage,  572 

Wild  carrot,  691,  708 

Willow  family,  667,  704 

Willows,  595 

Wind,  471 

Wintergreen,  709;  leaf  of,  43 

Witch-hazel,  706 

Wolfna,  28 

Wood-destroying  fungi,  553-555 

Woodland  formation,  516,  526,  529 

Xerophytes,  483,  485,  S65,  59°-599» 

618 

Xerophytic  structures,  487,  495 
Xerophytic  vegetation,  590,  594 
Xjlem,  50,  52,  360,  361,  363 
Xylogen,  92 
Xyridales,  703 

Yeast,  216;  fermentation  of,  115, 116 
Yucca,  394,  S6^  S^ST2,  7°3 

Zamia,  313,  316,  457 

Zannichellia,  627 

Zones,  525;  of  water  vegetation,  625 

Zoogonidia,  143,  149,  178-184 

Zoospore,  149,  154 

Zostera,  628 

Zygomycetes,  215 

Zygospore,  2,  138-140,  157,  160,  179, 

180 
Zygote  (zy'gote),  138,  179 


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OCT  28  1932 
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FEB  17  1933 

121933 


MAR  22  1935 
29  1935 


FEB  2  2  1937 


tfM  15  1938 
WAY  14  1S38 

JUN15  1939 
NOV     1  1949 


•4  J 

FEB  21  1952 

FEB  29    1952 
AUG  1  *  '960 

JL28'60GO 
DEC  1  2  1971 

FEB  1  4  1972  J  9 

APR  -a  1973 
MAY  4     197318 

KAY  20  1973 
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504782 


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